What I liked best about this game is that it surpassed my expectations so greatly that upon playing it for the first time (which was with SilkyBob), I went to the nearest store and bought it for myself.
The campaign never gets old, no matter how many times you play the levels over.
The weapons, the graphics, the gameplay itself; all of it is top-notch stuff.
Death animations are very cool, primarily consisting of ragdoll falls when it comes to the enemies. A new idea I've never seen so well-executed before involves the curb stomp, a way to finish off 'downed' enemies with your boot. Enemies can be downed if you shoot them in the knees; it's almost always what happens to players instead of dying (that way they can be revived by teammates or attempt to get up on their own).
Combat in this game is really cool. The controls seem complicated at first, but it's amazing how quickly you get used to them.
Once that's out of the way, the firefights are very intriguing and keep you yelling at your TV set the whole time. Yeah... I yelled at my TV a bunch of times... but let's not get into that.
Enemies are very brutal and scary, causing you to hate them and actually take pleasure in blowing them apart. They can be taken down using many different guns and melee attacks, including a chainsaw!
Blood and gore is maxed out, and the ground seems to be covered in red and orange pools by the end of the day.
Now to the best part of the game: the campaign. I have played the campaign quite a few times over (on different difficulties) and have not gotten bored even though I'm at the point where I can predict what the characters will say, and that's saying something!
You play as either Marcus Fenix or Dominic Santiago, both of whom are elite COG soldiers in a futile struggle against a strange alien swarm. This band of human brutes is one of the last human defenses against the Locusts, the strange aliens that live underground and emerged fourteen years ago. The Locusts are committing a terrible genocide against the human race, and the COGs have a plan to stop them. During the few days that follow, you will fight alongside other soldiers named Baird and Cole, and form a funny little team together. There are parts that are cool, parts that are funny, and parts that are downright scary, as the Locusts have an exotic arsenal of beasts that they will throw at you.
The multiplayer aspect of this game isn't that interesting (excluding the co-op campaign), mostly because games are small (about six people each) and rely more on squad tactics than insane killfests.
The game modes consist of things like deathmatches, 'protect the leader,' and a couple other that alltogether aren't that great.
If you get this game, it's definitely going to be for the campaign aspect.