[this is a no spoiler review]
Well, it wasn't terrible.
The first thing that impressed me was that the graphics appeared better than they did in the trailer - they were actually decent. I'm surprised they didn't beef the trailer up some more rather than creating the low-res critique-able render. They even blur for focus effects, which is a nice touch. While the graphics weren't up to today's standards for CG, it at least had a solid style that was watchable and enjoyable.
Sound work was excellent. High-quality, lots of effects. Even foot-steps when the camera is close. I must say I liked the sound of bolter fire, very intense. Even the score was well done and well placed. The voice actors were excellent and spot on.
Yes, there were glitches - inconsistencies in some of the camera work and lip-syncing was off here and there. These issues were mostly just at the beginning of the movie, as if they got better at it, and didn't go back to fix their earlier problems. Stairs seemed to be an issue as well, so most of the time they wouldn't show feet and stairs together. They didn't put the same amount of detail into the bad guys as they did the Ultramarines, which was disappointing because it made the lack of detail stand out. While the backgrounds are well done, fog is an easy way to avoid having to create actual backgrounds, but it worked.
Something that did bother me - and maybe it's just me - is the bickering, distrust and talk amongst the squad. It seemed more applicable to Imperial men, not highly trained Space Marine super-soldiers, even if it was their first run. (Though I haven't read much in the way of Space Marine books to know how they've established more of the fluff - maybe Dark Angels, which I have read, are just more hardcore than Ultramarines.)
I also can't help but wonder what a giant wooden bridge is doing at the entrance to a marine fortress on a desert planet with no trees. And what's up with the Chaplain's helmet changing colour from black to white later? Someone also forgot to tell them that cover saves are much more useful now. (I'm reminded of Sons of Anarchy when the big tough bikers just stand out in the open and shoot)
Overall, I wasn't wow'd, but it wasn't bad for a second (first official) Warhammer 40k movie. Voice acting and sound were solid, graphics were better than I was expecting from the trailer. Really, I think it was story and pacing that failed this movie. (which is unfortunately, since Dan Abnett is a well established author - my guess is his struggle came from fitting a story into an hour) I was reminded of the scene in Clerks 2 when Randal is complaining about Lord of the Rings being nothing but walking... except this was much less epic than LotR.
Verdict? Worth seeing - once. You probably won't watch this twice, so don't pay money for it - borrow it from / watch it with someone who is willing to part with the cash or split the cost between your gaming group.
[for those of you curious what I meant by "second" 40k movie and why you'll never see it (unless it's hiding in some corner of the internet)]