Gears of War has had numerous ups and downs the downs taking place near the end and the ups focusing in the middle. The number one up for the game, I think, is the gun executions, as they are unique to each gun and adds multiple neat ways of ending a enemies life. However the number one down to me is the removal of playing as locust in Gears of War: Judgment. The number one game to didn't have the most distracting Campaign, but had wonderful multiplayer options.
To me, the best Gears of War game is Gears of War 3, with wonderful Executions, and special game modes which let friends play together.