I haven't been this enamored with a game in long time. It combines some of the tactical elements of another favorite of mine, "Brothers in Arms," with the all out hectic nature of a good FPS. Add to that excellent controls, graphics, and music and you have a real contender for Game of the Year.
I think that what the game excels at is the little things. Sure, anybody can make an awesome next-gen game (well, anybody should be able to make a great next-gen game) but what really separates "Gears" are things like active reload.
Tired of just regular reloading in games? How about integrating a quick little minigame into ths normal action? Press the reload button once. Under your gun, you'll see a little white bar move from left to right. Press the reload button again to make the bar stop in the designated area and you'll reload faster. If you stop the bar in exactly the right place, you get temporary boost to damage (think of the mechanics of a video game golf swing before analog sticks came into play). As you play more and more of the game, this becomes an important part of your battle technique. In fact, I have the timing committed to memory so that I don't have to look at the bar. Getting that temporary damage boost really comes in handy.
The game also has excellent weapons, but not so many that it's overwhelming. The Lancer Assault Rifle has a chainsaw bayonet standard, so you can run up to any enemy and slice them. The shotgun works well, grenades are fun to throw (they're like chain grenade that you swing and whip), and the Hammer of Dawn, a weapon that fires down from a satellite...you aim it.
Another element that "Gears" has done right is the cover system, which allows the player to dive, move, and swat turn from one piece of cover to the next. The game designers have strategically placed cover in every room of every level. This is all done with the "A" button, meaning that it becomes second nature, and it better or you'll quickly become grub eats.
Other things the game got right: Third person over the shoulder view (I so much prefer it to first person). Quick weapon inventory system with the ability to carry only four weapons. A Halo-esque health system where there is no "health meter" or health packs, just a damage circle that appears when you're hit. The more it fills in the closer you are to death. Take cover and the circle goes away.
I think the only thing that I wish was a bit more fleshed out would be the squad commands. Being a huge fan of the "Brothers in Arms" series, I enjoy the control of two teams whom I can send anywhere on the map. In "Gears", you can do the rudimentary regroup, be agressive, or be defensive commands. To the average gamer, I can see why you wouldn't want to complicate this, however, I feel that most gamers won't even know squad commands exist.
The genius of "Gears of War" is its simplicity (this is often the case with great games, think "Shadow of the Colossus"). Nothing is overwhelming and all of the game elements are well thought out. Nothing feels cumbersome and nothing gets in the way of enjoying the game.
I have yet to play the multiplayer, but I'm sure that will be of high quality as well.