As with previous books, I'm really liking the new codices. The hard-back format feels nice and the quality is pretty surprising and satisfying. While the books are expensive, I don't feel like they're as overpriced as the price tag might indicate; the artwork is beautiful, the books are well designed and have a lot of background and fluff. As mentioned before, while there is a good bit of Ultramarine focus, it's more equally divided. I haven't read it in detail, but there are 4-10 pages on each of the first founding chapters covered (Ultramarines, White Scars, Raven Guard, Salamanders, Imperial Fists, and Iron Hands) as well as several pages on the big successor chapters (Clemson Fists and Black Templars). More minor successor chapters get about a half page each.
As far as new rules or rules changes, most have been mentioned online, but I'll run through some here:
Centurions: The much debated unit, mostly because of their appearance, these guys look to have some solid rules. The Assault squad comes with siege drills, which are not unweildy, but S9 AP2 and have Armorbane. With 1 base attack, they get an additional for two specialist weapons, and can pack a punch. Not to mention, they have the decimator protocols (fire 2 weapons) and flamers, which can be upgraded to meltaguns. It will be interesting to see if they get put into Land Raiders to get closer and take down MCs and other big, hard enemy units. The Devastators can put down a lot of fire, but the upgrades make them extremely pricey (a regular devastator squad with 4 Flakk Missile Launchers is cheaper than base Centurions).
Hunter/Stalker AA Tanks: Both of these tanks have the limitation of not having interceptor, meaning they can only snap shot at ground targets. This makes them very much one-trick ponies, but they're both extremely good at their role (which is more or less a theme of the codex). The skyspear missile launcher (single shot AA) is interesting in that it can home in on the target if the shot is missed the first time. A missed flyer gains a homing token. In each subsequent friendly shooting phase, the missile hits on a 5+. The only way the target can remove the tokens is to fly off the board or get into combat. This definitely is a cool little dimension, and could help deter flyers into flying off to avoid missiles. The other AA weapon is more or less a quad gun, though you can chose to give up twin linking and fire at two targets at BS2.
Changes to Equipment/Units/FOC
Auspex: Not a new unit at all, but I believe this is a new feature: an auspex user can choose to "shoot" a unit within 12" with the Auspex (and can be a different target than his unit). The targeted unit has its cover saves reduced by 1 for each auspex used in this way.
Camo Cloak: Camo cloaks give +1 to cover, not Stealth, so it will stack with stealth.
Cluster Mines: Make a nominated terrain piece dangerous for the battle
Techmarines: Techmarines are now a non-force org unit, and can be taken for each HQ choice taken rather than an elites choice.
Land Speeder Storm: Now a Dedicated transport for Scouts, not a FA choice.
Vanguard Veterans: Moved to the very crowded Elites section, though this means you can potentially have 6 Jump Units in your primary detachment.
Thunderfire Cannon: Gains Barrage on all fire modes.
Chapter Master: +1 W and A, -5pts
Other Generic HQs: All cheaper
Tac Squads: Much Cheaper
Razorback: up in points, but options are cheaper
Most units in the army are a bit cheaper, though options might be increased cost.
Chapter tactics is one of the big changes to the book. While the rules themselves are generally fairly minor, they look like they will do a great job of adding unique flavor to different chapters. Some of the strongest, I think, will be Imperial Fists and White Scars. Bikes are already good in 6th, and White Scars bikers get a good bit better. I also like Raven Guard's, which gives Scout to non-bulky units, and Jump units can use their packs to move and assault, rerolling to wound with Hammer of Wrath.
The other aspect of the Chapter Tactics is that it allows Space Marine chapters to ally with other chapters. This could lead to some interesting combinations, and I'll be curious to see how this shakes out.
I'm not a Space Marine player, so it's hard for me to judge, but one thing I like about the Chapter Traits is that I think it encourages playing your own chapters. In particular, it could be fun to try out different Chapter Traits, with different "companies" in your homemade Chapter getting different chapter tactics to indicate a specialist-style company. This could be used by a crafty or disgruntled Dark Angel player to make their own chapter, with Ravenwing using White Scars tactics, while Deathwing or regular troops could take Imperial Fists or Ultramarine traits. Just a thought.
This is by no means a detailed or complete review of all the changes. That said, the biggest impression I've gotten from my first read is a bunch of small changes which allow for very divergent builds that are viable, which I think was a major goal of the new codices, and something I'm really liking.
For those of you that have the 'dex, what do you think of the new book? For those of you who don't, what thoughts, questions, or concerns do you have?