Not a very impressive book overall. Some units get changes, but a lot of them are are either changed for the sake of change or ridiculous nerfs to units that didn't need them. Proof reading is sketchy. For example, one of the DKoK assets gives units fleet, but only for the movement phase when they can't actually use it. And the Vraks warzone is underwhelming. It's not bad if you're going to buy the book anyway, but you're not missing anything if you never read it.
Imperial Fortress: it does stuff. Too bad none of what it does matters because it suffers from the same problem as every other massive fortification: D-weapons destroy it on a 2+. That's right, your $1000 500-point fortification that takes up half the table will be killed in one shot by any random titan that feels like getting rid of it. If you're even thinking about getting one of these you need to talk to your fellow players and figure out a house rule to fix this insanity. A good starting point is probably ignoring the rules in this book and going back to the last version, where it has SP like a superheavy vehicle.
Heresy units in 40k: with one exception (see below) these seem to be a pretty straightforward copy/paste from the Heresy rulebook with the minimal changes to match the new superheavy rules. This is a pretty compelling argument for just allowing all Heresy stuff in Apocalypse games.
Cerberus and Valdor: the shock pulse rule is significantly different now. Instead of just stunning any non-superheavy vehicle hit by the main gun you now force them to fire snap shots next turn if you get a penetrating hit (this explicitly includes superheavy vehicles). So yes, a single Cerberus has about a 50/50 chance of turning an emperor titan into a useless paperweight for a turn.
Contemptor dreads: lots more options now. You're no longer stuck with a DCCW, C:SM dreads can now take melta guns in their DCCWs, cyclone missiles are cheaper, etc. It's not quite "if you can build the model it has rules" now, but it's pretty close.
Valdor: loses D3 shots that it had in IA1(2nd), which means if this isn't a typo the Valdor is back to being utterly useless. Sure, you can shut down a titan, but you have a 75% chance (BS 3 and rolling against AV 14) of doing absolutely nothing with the one shot you get before a D-weapon removes your tank from the table. Which makes me sad since I love mine and never even got to use it with decent rules. If FW doesn't FAQ this be nice to the poor Valdor owners and let them use it as a Cerberus.
Hell Raker assault battery: nice improvements here, the second command tank option is now a Stormsword (much fluffier and better rules) and the 10" combined shot is now AP 1 (much more powerful when you're removing enemy artillery parking lots).
Macharius Omega: First of the units that the author of this book clearly hates. Apparently having a worse version of a plasma blastgun that gets hot if you try to use the large template wasn't enough, the poor Omega gets crippled with a special version of 'gets hot' that inflicts D3 glancing hits instead of one. Take pity on anyone who bought this model and let them use it as a Stormblade, and wonder why FW keeps making random stupid changes just for the sake of doing something new.
Marauder bomber: ugh. This is a mess. The rules are completely different from the ones included in the special edition Apocalypse rulebook. The IA one gets better armor and much better conventional bombs, but hellstorm inferno bombs instead of the 7" blast. Fortunately Marauders seem to be rare, but if anyone is bringing one you really need to make a house rule about how to handle the conflict.
Marauder Destroyer: don't like the Marauder controversy? Just give the Destroyer more than three times its former bomb load. You barely have fewer bombs than the standard Marauder, but get all the extra guns and hellstrike missiles as a nice bonus. Thank you FW for giving me some more encouragement to build mine!
Imperial Navy heavy bomber wing: overall a dull formation (bonuses to weak bombs), but this is the textbook example of a formation that only exists to unlock the formation rules. Do I care about the special bombing run rule? No. Do I want to buy a second Destroyer so I can fly them in formation and get tank hunters? Yes. Consider this an example if you're planning to design your own formations, in Apocalpse 2.0 just being a formation is a powerful bonus even if the special rules it grants are worthless.
Chaos Reaver/Warhound: GOD-SPECIFIC BONUSES. All of them make it a demon and give hatred against the enemy chaos god. Khorne gets bonus attacks when charging, Nurgle gets IWND, Tzeentch gets to re-roll 1s to hit (and depending on your answer to that controversy, effectively twin-linked blast weapons), Slaanesh gives fear at a -2 LD penalty.
Demon Lords: Everyone gets a 3++. Angry becomes a flying gargantuan creature. The giant bird is a FGC, ML 4 psyker (2+ rolls on tzeentch, rest on any single core rulebook table), needs to pass its DTW roll to reflect psychic powers, and gets haywire hits on its shooting attacks instead of pens on a 4+. The nurgle one now only doubles melee wounds on a failed toughness test. The slaanesh one gets to regain a wound on a 2+ if it inflicts any unsaved wounds in combat.
Necron City of the Dead: stupidly expensive (both in points and money) fortification made out of four ROB tiles. Gives out a bunch of rules if you're the one person who can actually put one of these on a table, and your opponents don't tell you to save it for a theme game.
Pylon Network: cover save based on the number of other models from the formation within 12", up to a 3+. Considering how rare cover can be on many Apocalypse tables this is a pretty nice one if you're willing to put lots of your pylons together and risk the inevitable template shots.
Cobra: Lucky winner #2 of the "the author really hates you" award. Loses 12" of range, the barrage rule (no more targeting out of LOS), and is down to a 7" blast. Oh, and to add insult to injury you get a small point increase. Sure, you get AP 1 on the main gun now that it doesn't matter anymore and the template remains in play on a 4+ and counts as dangerous terrain with no armor saves allowed, but that doesn't make up for losing the 10" blast.
Lynx vs. Scorpion: the Scorpion now has a purpose again. The Lynx is down to AV 11 and keeps its optional flyer-that-can't-shoot rule, the Scorpion stays AV 12 as the more durable tank. You could argue that the problem should have been handled by boosting the Scorpion instead of nerfing the Lynx, but at least now there's a reasonable argument in favor of taking each of them.
Warp Hunter: I'm starting to think someone at FW hates Eldar. The main gun is nerfed to STR 7 AP 3, loses the "torrent" rule on the flamer option, and loses 12" of range on the blast shot. Now instead of an awesome tank that makes Vindicator drivers jealous you get a redundant MEQ killer. Maybe you can pretend they're Wave Serpents and still use the model?
Hornet: the one bright spot in the Eldar mess. Base price goes up a bit, but weapon prices go down significantly (for example, pulse lasers from 30 points to 5 points!). It probably won't matter much in a big game, but if you play Eldar in standard 40k you're going to be happy.
Skyscythe Slaughter Host: AKA "buy our big expensive models". 2+ units of warriors each in a Tantalus, 1+ Reaper. And for all that money you get to deep strike with no scatter and still move at combat speed, and you drop an apocalypse barrage with haywire and shots/strength based on how many vehicles you have in the formation. Unfortunately it's AP 4, so its usefulness is going to be pretty limited. And amusingly you only get the barrage if you have a Reaper in the formation, but the Reaper is a 1+ option. Yay editing?
Lifta Wagon: big nerf here. Has to roll to hit (at BS 2), can't fling anything over 4 HP, and loses the one-shot D-weapon option.
Big Squiggoth: major changes. No longer a dirt cheap MC, but gains a better stat line and a combat drugs table.
Tiger Shark AX-1-0: no rule changes since IA3, but if you haven't seen that book yet the Tigersharks are much better, with AV 12/12/10 and BS 4. Also, the railshark is obviously a titan killer but don't forget that it has one of the few skyfire D-weapons in the game, so if the Tau player wants air superiority they're removing any non-superheavy flyer on a 2+ with a salvo of seeker missiles to take down a second target.
Tau Titan-Killer Cadre: the railguns get a useless ability to knock down a void shield and hit the next one (or armor) on a 4+, assuming you're stupid enough to waste D-weapon shots on void shields instead of dropping them first. But what really matters here is you get to declare a primary target and get D3 VP if you kill it. So if you're willing to "waste" a round of railgun fire you can target a Malcador and pick up the easiest D3+1 VP in the game. Oh, and if you fly in formation you can throw tank hunter seeker missiles at something else while you do it.
Hierophant Upgrades: some interesting stuff here. Incindiary ichor drops a pie plate of automatic no-armor-save wounds on any model that dares to inflict a wound on your titan in assault (say goodbye to your whole squad). Swarm incubation chamber makes it a 20-model transport. Spine-cloud spray gives it a decent AA weapon. Bio-plasma gives you an AP 3 hellstorm. Spore mines gives you a STR 4 AP 4 apocalypse barrage with 8 shots.
Warzone: Vraks: brief summary of the fluff, and new rules + missions for playing in the setting. Also, some of the characters get updates that can be used outside of Vraks, but none of them seem to be particularly interesting. Annoyingly the DKoK get a fluff character and finest hour, but no rules for him. WTF.
Disasters: they exist, they kill stuff. I hate the entire idea so I have no idea how they compare to other disaster tables.
Finest hours: Zhufor makes everyone who can see him fearless if he collect's a character's skull. Hector Rex gets rampage, a 3++ and multiplies unsaved wounds to D6 against a chosen demon lord (and he already wounds them on a 2+), but only if a demon lord is on the table. Good luck getting him into combat alive though. Arkos has to use his finest hour from reserve, and immediately deep strikes with no scatter and can assault (IOW, his terminators remove a unit from the table). Colonel Tyborc (Krieg character, just give his name to a standard codex or DKoK CCS) has to be within 6" of an objective and gives his unit and any DKoK FNP (3+) and himself IWND. Too bad pretty much everything in Apocalypse ignores FNP on a T3 model or this would be a pretty nice way of keeping an objective secure.
Ranging Barrage (strategic resource) adds 4 Basilisk shots to a barrage after resolving it, which means less damage than the standard bombardment asset but at least it won't scatter if you like the impact point on the initial shot.
Chemical Warfare (SR) shows that FW doesn't actually play the game they're writing rules for, since it gives gets hot and fleshbane to a unit with blast weapons when every blast weapon in Apocalypse is already wounding on a 2+ 99% of the time. But at least you can keep it and use it again every turn while the rest of your team yells at you for wasting VP.
A Schedule to Keep is a complete WTF. All DKoK gain fleet for the entire movement phase. Does anyone even try to proofread these books?
Tunnel Warfare is awesome. Bring a unit in with no-scatter deep strike, and if you do it within 1" you lock in combat with charging bonuses. IOW, pick an enemy unit and remove it from the table.
Burn the ground, blacken the sky is fun if you like disasters since you get twice as many. If, like me, you hate disasters then this is a waste of paper.
Consecrated in Blood and Death gives demons that arrive from deep strike a 3++. Use is obvious.
Sanction Extremis (SR) lets a GK unit shoot a 7" blast LRBT shot. Why you would ever use this instead of a standard orbital bombardment, I have no idea.
Xaphan the Savior gives one formation FNP (6+) and fearless. I suppose this is useful if you forget that attaching a commissar to a unit already gives you a 99% chance of passing a leadership test and still lets you go to ground behind your ADL.
Angels of Death is fluffy but useless unless you ran out of drop pod models. Put an apoc barrage template anywhere you want (with no scatter), then put a deep striking and now fearless space marine unit on each of them.
Missions: fluffy, but they have lots of weird rules and don't seem to be very carefully balanced. They're intended for 5-7000 points a side and probably shouldn't be played above that level. I'd hate to play an entire 500,000 point game and discover that the mission was over before it began because the victory conditions were stupid. TBH the best use of the missions is probably inspiration for your own ideas designed to match the armies in your specific group.