I just finished Warhammer 40,000 Space Marine. I thought it was fairly decent, but it has a lot of little annoyances that will dissuade me from ever touching it again, like getting stuck on terrain and unresponsive keys.
Story is okay, it got me curious about other games in the Warhammer 40K universe, but it certainly isn't the greatest thing ever. I really like the main character; I enjoy playing as someone that seems to be in charge, rather that just following orders from whoever he comes across. Most of the other characters are quite forgettable though.