Got my review copy three days ago and I steamed through the campaign. I really can't wait to do it again. The single player is heads and tails better then the first game, and the first one was really good. Graphically the game is amazing as well. They stuck with the same general art and feel, but they added enough color and detail to make it look a lot better. Don't believe whomever posted the article about the game looking washed out, IT DOESN'T....ITS GORGEOUS! He was obviously some idiot fanboy.
The campaign is a bit longer, probably 3 to 4 more hours, depending on what difficulty you play on. The biggest change is the story. This time around you really have a strong narrative to hold you through the game. I found myself really drawn into the story this time and it will tug at your heart, if you have one. I would say more but I don't want to ruin the story for anyone.
I ran through the game with a friend and the co-op is rock solid. We played the entire campaign over three days and we never once lost connection. This may vary for people with bad connections though. You should play this game in co-op, there is much in the way of game design that makes the game better when friends are involved.
The one thing I really like is the fact that the game will now track every achievement for you. This is a nice feature that should be in almost every game from now on.
The MP in Gears is where I really give Epic a lot of credit. They listened to what was wrong in Gears 1 and they made the MP 100% better. The matchmaking system works as well as Halo 3's, The new gametypes are fun and really imaginative, and the included maps are all well designed and balanced. In my play so far I have yet to play a map that I disliked.
If you own a 360 get this game!