First of all, I'd like to preface this review in all fairness by saying that I only played about 40-50% of the total campaign. From what I did play, it was repetitive and kind of predictable, but I think if you're not overly picky about what games have to offer you'll like this game.
I had heard from someone that they were getting this game and that particular person is very picky, so I decided to give it a shot just based on that. I didn't know anything about it and if I had to describe it I would just say that it's basically Gears of War with space marines. It's a solid 3rd person shooter, but nothing I would ever spend money to buy, although I do admit playing it with the volume blasting made it a lot of fun.
If you're trying to make a choice between this game and another game, I would say that this is something that you can probably wait to play. I think it'll be in the bargain bin in a couple months.
I like this game very much. The characters were what you would expect to be in the Warhammer universe (except for that one Space Marine that followed the rules to the letter). Great graphics and detail to the environment, but I was really hoping to go to another planet and not just be stuck on the one. Plus, the game just had you going back and forth. "Go to the Manufactorum! Go to the lab! Go back to the Manufactorum! Fight to the Tower!" That kinda irritated me.
Fighting was solid. The support NPCs (except for the non-SM guards and their little laser guns) actually did damage and helped you out when you weren't going solo. Weapons were amazing and you had to make almost every shot count for you to actually live in a long battle (because executions wouldn't keep you up forever and just rushing in all the time was a bad idea).
Multiplayer isn't too bad, just wish there was a little bit more diversity in the way of maps and a few bigger ones, too. The classes for multiplayer are awesome, but some of the guns are very over-powered (Plasma gun, anyone?).
Overall, I was very satisfied. I wish I could have gone somewhere else other than Ajakis, like back to Terra or Luna, and maybe met up with other Space Marine chapters, but I'm not complaining too much. I had fun.