On Amazon and even in GAME you can pick up "Space Marines" for £ 12.00!
This game is awesome bloody fun. AI is smarter than you might initially give it credit for and even though you're essentially a genetically overmodified human tank you'll still have to stop and look both ways before you leap into the throng of battle.
Great shooting. Awesome bludgeoning and eviseration. Lovely explosions.
Free DLC for coop play. Free DLC for Extra game modes.
There's some chargeable DLC just out now to let you play as "Chaos Marines" but you're not missing out if you don't have that.
If you don't have a copy of "Space Marines" get one now. There's no excuse. It's a great game.