Gears of War combines a great story with fantastic action
I think one of the biggest developments in the game is your ability to hide, and then choose to peek out for a better shot or simply let the bullets fly in your enemies general direction. If you manage to keep your enemies at a distance it's relatively easy to pick them off. Eventhough on Insane difficulty they're pretty good shots and almost invariably aim for you, it's still not overly challenging. When enemies charge you however, it's much more difficult. They'll almost always force you to get out from your cover for a melee attack (preferably chainsaw). This leaves you vulnerable for other enemy fire, and it doesn't take much to put you away on the harder difficulties.
Overall controls are fantastic, there are lots of options as far as what you would like your character to do at any given time. Whether you want to jump a barricade and charge the enemy or move from one side of a doorway to another, it becomes second nature very quickly.
Weapon selection was pretty good. The bow with exploding arrows is a fantastic weapon. Also, the ability to reload faster with the push of a button at the appropriate time is a life saver. It might take a bit of practice and frustration, but you'll get it eventually.
Overall, it's a fantastic game and I can't wait to try the second one.