Mass Effect 2 does an absolutely amazing job of mixing great gameplay with an epic story. The story is strong and extremely well linked to the events that occured in Mass Effect.
The gameplay has been changed quite a bit but its for the better. The combat is intense (the introduction of hot keys means you don't have to pause the combat to use powers), well-paced and there is a good amount of it. Overall I think this game is a must have for anyone who has played and enjoyed Mass Effect or likes Biowares other Rpgs.