Space Marine is about as simplistic as current generation games get. As Captain Titus (Mark Strong, the narrator of Who Do You Think You Are?) all you really do is go forward and shoot/duel, and it's a long game with nothing much sustain the many miles of bad road. For a 3rd person shooter it's basic stuff. Set on a distant planet filled with Orks it is your duty to wipe them all out. The levels/chapters are very slow, with huge, cavernous empty spaces and bombed-out buildings that offer no interaction other than occasionally opening a door or elevator. Half of each chapter will involve you doing nothing but moving forward.
If it were not for the Warhammer brand name this game would be the very definition of shovelware. I played it right to the end, unlocking 34% of the trophies, but to get the platinum you'd literally have to spend over 100 hours playing this game. Quite frankly, I don't want to know anybody who commits that amount of time to a video game, or indoor activities in general.
