Gears or war is a great game with alot of depth if you take the time to play it
First off the campaign mode, while not giving too much story itself, is good. Its not very long and you can get through it in insane in under a day. That said what is in it is amazing. Great firefights make it interesting the whole way through with little room for clam moments.
The mulitplayer is where most of the fun is at with constant action, where if your not shotgunning someone. then you will be shotgunned yourself. The MP is great fun and will last you a long time.
Altogether Gears of War is great game and one you are likely not to forget soon.