Shallow campaign mode coupled with fun although unoriginal multiplayer.
In Space Marine, you will step in to the role of one of the titular super-soldiers of the Imperium, wielding exotic future weapons as you battle against the Orks on the surface of Forge World Graia. As the experienced, unorthodox Captain Titus, you will blast your way through tiny gretchin and giant Nobz with your sergeants, Learchus and Sidonus.
Although the blue and gold armor of the Ultramarines and bright glows of energy blasts do present some very pretty sights, it's worthwhile to note that almost everything else in the game is brown, grey, or some variant thereof. Even your enemies, the greenskins, seem to have been colored with the dullest, least-interesting shade of green possible. This is a sad result of being created in the modern generation of gaming. But, other than the limited palette, the graphics are fairly high-resolution.
Also worth noting is the fact that the entirety of the campaign only takes a total of nine hours, even with the optional search for the hidden audio log collectibles. Those looking for their money's worth in the single-player experience may find this rather disappointing. Although short, the campaign provides fun, enthralling moments, such as chasing a teleporting Ork shaman around a huge arena using a jump pack.
And now we come to the multiplayer, which is apparently the intended meat of the game. Instead of a server list, you are presented with a matchmaking lobby, where you select which game type you wish to play and wait for a suitable room to be retrieved for you. This is frustrating, as it is entirely possible to spend ten minutes waiting for a match that may never show up. The PC port of Halo: Combat Evolved had server lists, there's no reason this game cannot.
Multiplayer in Space Marine, discounting the dreadnought DLC which I do not have, consists of a grand total of two modes: team deathmatch "Annihilation", and 'small group of players versus hordes of computer enemies' "Exterminatus". While both of these modes are very fun, you will soon be sorely wishing for more variety, even with the three distinct character archetypes to choose from: the all-around Tactical Marine, the fragile, speedy Assault Marine, and the heavy-weapons user Devastator Marine.
There is a level-up system in multiplayer, whereby you gain abilities and wargear for your character to use, as well as cosmetic bits and pieces with which to customize your avatar. Also available is a large list of pre-set paint schemes and iconography, based on Warhammer 40k's diverse Space Marine and Chaos Space Marine chapters/legions. While obtaining all the bitz and gubbins is fun, it's not enough to significantly expand the lifespan of this game.
Overall, Warhammer 40k: Space Marine is an average game. The single player experience, while hardly your money's worth, is a decent distraction from a functional, if unoriginal multiplayer shooter. For fans of the 40k franchise, this might be worth a look, but those looking for a long-lasting experience may wish to put their money on other titles.