Ultramarines is based (thematically) on a futuristic tabletop wargame, Warhammer 40K. The Warhammer 40K universe is a heavily militarized, Gothic styled fantasy universe that masquerades as sci-fi, while keeping all the common fantasy tropes. Its main attraction are the human super soldiers "Space Marines" - basically medieval knights in space and their fight against "enemies of the imperium".
Ultramarines depicts that fight in a small scale, through one mission of the Ultramarines chapter (fraction within the SM). Unfortunately the universe is very badly conveyed and the storytelling scope is so limited its obvious that the primary target of this film are the fans of WH40K.
As it stands they are the least likely to be pleased with the outcome. What is shown is one uninspired mission, loaded with every cliché imaginable, gripping a terrible script (although the actors made an effort) and wrapped in outdated CGI.
Its like a single episode of a TV series, or a comic book in terms of storyline and characterization - a part of a whole that never comes.
As a passive fan of WH40K I really wanted to like Ultramarines, but apparently it had neither the budget nor the creative drive to truly embrace the universe that its supposed to portray. Instead its a routine military/horror flick with characters you can't tell apart and a story you will not care about.
Skip it.