The announcement trailer suggests Gears of War 3 will be the end, and Microsoft has now confirmed this to be true. However, while Gears 3 will be the final game in the Gears of War trilogy it doesn't mean we won't see more from the franchise in the future.
In a press release confirming the game's April 8, 2011 release date, Microsoft stated: "Gears of War 3 plunges players into a harrowing tale of hope, survival, and brotherhood that will conclude the current story arc for Gears of War."