I'm one of the people who loved the finale of the Sopranos the other night. I felt the entire show was in keeping with the character of the entire series, and that the ending, while ambiguous, was spelled out clearly enough to provide the show with some closure. It just takes a little thought to put the pieces together.
Personally, I subscribe to the theory that Tony was whacked at the end. In the second-to-last episode, there was a deliberate flashback to a conversation between Tony and Bobby (who had just been whacked), talking about what it must be like to be killed. Bobby's point was that one would probably never even hear the bullet that did the job.
To me, that means Tony never saw or heard it coming.
A second train of thought that popped into my head is that, if Tony is still alive, the last five minutes of the show is some masterfully done television that conveyed, for a few seconds, what it must be like to be Tony. The tension that the viewer felt while watching the end of the show, waiting for something to happen and not knowing where it was going to come from, must be a lot like the minute-to-minute existence of Tony himself. He's always looking over his shoulder, always a marked man, never knowing when his life of crime is going to catch up to him.
Either way, I loved it.