This movie is a terrible incarnation of the Warhammer universe. The characters all look the same, the settings are practically nonexistent, the action is dull, the dialogue is terrible, and the plot is boring. This film is like watching an extended and unfinished cut scene from an old videogame. The visuals are so poor in comparison to similar films! Compare 9 or Toy Story or even Spongebob Squarepants!!! There is a lot more detail in both the foreground and background.
If you are truly interested in the Warhammer universe, buy the books. There are short stories in the series that easily eclipse this movie.
Deathwatch (Warhammer 40,000), Way of the Dead (Warhammer Novels), The Ultramarines Omnibus (Warhammer 40,000 Omnibus), Crucible of War (Warhammer 40,000 Novels), Bringers of Death (Warhammer 40,000)
Also, if you want to enjoy a much better story with MUCH better visuals, and actually play through it, I recommend the videogame Warhammer 40,000: Space Marine. On PC or console, this game has a better story and is a lot of fun to play.