Warning: All of my reviews may contain spoilers!
It was almost a no win situation for Gears of War 2. The original Gears is one of the 360's signature titles, so the expectations for the second game were as high as could be. In addition to that, Epic Games had to finely balance pleasing fans of the original, while also implementing new ideas and fixing problems that stood out in the original.
They
just about managed to do all they set out to.
Gears 2 once again follows the story of Delta Squad, a group of battle hardened soldiers in the C.O.G. army that are fighting a never ending battle against the Locust Horde. The story picks up right after the ending of the first game in which it was assumed the Locust were wiped out, but in true action movie style they are back and more aggressive than ever. They have recently started sinking entire human cities underground and humanity is on it's heels, it's up to you as Marcus Fenix (or Dominic Santiago in co-op mode) to shoot, shotgun, blow up, scorch, and chainsaw as many baddies as you can for the very survival of the human race.
If the story sounds derivative, that's because it is. Cliff Bleszinski, the game's lead designer has even said that his goal is to make you feel like you are the star of a summer action blockbuster. The nice thing about the story is that it serves it's purpose exactly as it should: it does enough to make you want to see where it goes and to keep the game moving along, but it never bogs things down or gets boring. Indeed you could even ignore the story altogether and still have a great time just blasting your way through the campaign.

As for the gameplay itself, the core of the game remains the same. Namely, you either stay in cover and lean out to fire, or you die very quickly - this is not a game where you can run and gun and expect to survive. The cover system has been greatly improved, no longer will you get stuck behind a wall with no easy way to move out, becoming easy prey for the enemy. The shooting is still visceral and fun, and every weapon save for maybe the standard issue pistol are powerful and fun to use. Large scale firefights happen early and often, there are bosses aplenty, and quite a few nice set pieces that add to the variety of the levels. The vehicle sections are much improved from the first game, and while still not perfect, they do add some variety to the campaign.
The campaign isn't perfect though. There are several timed events which are not clear the first few times what exactly you need to do to complete them. It's quite frustrating to only have 1 or 2 shots at completing the event and if you fail, it's game over. I don't understand why these are in a game that rewards careful strategic thinking when it comes to large fights against a a foe that outnumbers you. These events must be carried out to perfection in a short amount of time or you fail, it's oddly out of place. There are also some head scratching platforming sections in the game. While not too challenging, they really seem to stick out like a sore thumb in a game in which the main gameplay element is shooting bad dudes.
Gears 2 looks great, in fact it is the nicest looking game I have seen on any console. While it's not a giant leap in graphics from the first game, it is still very, very impressive. One of the nice touches is that it addresses many of the complaints from the first game, namely that it was too drab using too much gray and brown. Many of the outdoor areas in Gears 2 are green fields and snow covered mountains, adding a nice amount of color variety.
Multiplayer has all of the modes carried over from the first game but with the addition of one more player making the standard deathmatches 5 on 5 skirmishes. You can now play locally with AI bots which makes the multiplayer much more viable to play if you have some friends over. However, the real shining star in Multiplayer is the addition of Horde Mode.
The idea of Horde Mode is simple: wave after wave of Locust descend upon you and up to four teammates. After each round, the Locust get tougher and more and more show up. Up until about the 5th wave, you can go out on your own and do pretty well, but after that you have to work together if you expect to survive. Horde Mode is simple, fun, and addictive and has proved me many hours of gameplay long after I had finished the campaign.
Gears of War 2 isn't a revolution or reinvention of the first game, it's simply a refinement and improvement of all the things that made the first game great.