Space Marine is the first deviation from the RTS series, and actually is better than expected.
The Bad: Same enemies and combat forever, no intense scripted events, can't use the Titan, multiplayer gets boring after awhile, only two modes, gets extremely difficult towards the end
The Warhammer series, being an extremely expensive table top game, has grown to be more popular as an RTS game than anything else. Space Marine is the first outing out of the genre, and with lots of speculation, was deemed to be a complete failure. Relic proved everyone wrong by delivering a good game that has tons of action, gore, and a good story that the RTS games pack in. You plays as Captain Titus of the Ultramarines. You are the leader of the elite force who are part machine and can take out whole battalions of troops that regular marines couldn't. The Space Marines believe in a religion of the Machine God and anything else that isn't machine related is heresy. You, and your three squadmates, are fighting back the Ork invasion and are trying to reach the Titan Manufactorum that holds the most powerful war machine ever built. On the way some weird twists happen and you end up fighting the Order of Chaos and Daemons towards the end. How that happens I'll let you find out for yourself.
The story is decent, not very deep, but its entertaining and the voice acting is superb. Relic got the art style and feeling of the Warhammer universe across, so the game looks good, but technically its nothing special (using the Unreal Engine 3). The fighting system goes two ways with melee weapons and guns. There are a lot of cool guns to shoot and they are unlocked slowly throughout the campaign. They each feel different and powerful and you have to mix up your strategy of how you're going to use what weapons for what situation. You can't just use the same ones through the whole game. The melee weapons are less in numbers but just as cool to use. The chainsword allows you to tear enemies to shreds and executing awesome kill moves is fun. This is actually how you get health, but its flawed in a way. When no ground enemies are around you can't heal and have to rely on your shield charging, so it's a unique idea, but we need a way to heal up when fighting aerial units. You also get to use the Thunder Hammer, and the Axe which are all great weapons to use, but the hammer only lets you use the pistol and bolter, so no heavy weapons can be used (I'm assuming a balancing issue).
While you chopping down Orks by the dozens you will get to use the jet pack a few times. Launching into the air and pounding the ground while enemies fly around is great, but you don't get to use it enough. What is enough (actually too much) is everything else. The same Orks come at you through 2/3 of the game and the same execution moves are repeated over and over again. By the time you get 1/4 of the way through the game you wonder if there is anything but Orks that exist. A few different types show up throughout, but not many and the game just gets harder and harder as you go along instead of throwing in variety. Towards the end you can't really do much melee and you start relying solely on guns because charging in will just get you killed. I didn't like this form of balancing because melee is much more satisfying and fun then shooting everything.
Overall, the game would have been even more amazing if there were some scripted events instead of just the same run and kill scenario over and over until you puked. The muliplayer is ok, but just has two modes and gets boring after a while because it's the campaign, but with human players. I loved the characters, story, and world of Warhammer, but let's add some more depth to the action, some more enemies, and make the game feel more intense besides ramping up difficulty. We didn't even get to use the Titan! Sure you get to be on top of it for a few minutes, but these are the events we need to make Warhammer an amazing action experience.