Mass Effect 3 is the third game in a trilogy. The game builds upon the events of Mass Effect 1 and 2 like no game has done before.
There has been a lot of talk about the ending and I'll agree that it was unsatisfactory but the game itself as a whole is still a 5-star product. Do take into account that Bioware are attempting to rectify the ending with an 'Extended Cut' DLC pack that will be released for free quite soon.
The soundtrack is amazing, the combat is amazing, they've added more guns, you get to see new planets/species that were not fully introduced, a lot of things are wrapped up...
It comes down to if I'd recommend the game to someone or not and I most certainly would, no question about it. The fact that so many people are in an up-roar about the ending just shows how deeply engaged the game had people within the story.
Buy the game, support Bioware.