I've been holding off on doing a post on this one, but finally decided to give in and throw in my two cents.
I loved the ending, and I may be the only one who thinks it was clear-cut. Immediately upon watching it, I thought "Holly shit, they killed Tony." I actually jumped in my seat when the screen cut to black. Since he WAS the show it just makes sense that there would be nothing left to watch once he was gone. I've had some time to think about it, and I stand by my initial reaction. He's dead as Di dropping downers at a disco.
Earlier in the season when Tony was in the boat with Bobby he had said something to the effect of "I don't think you ever see it coming, All of a sudden everything just goes black" - I'm paraphrasing, but you get the point. They also did long black holds last season when they were cutting between his "everyman" coma fantasy and the waking world, so after the 5 second ending of blackness you could legitimately insert Heaven, Hell, Tony stuck in a hotel as a businessman without his wallet, reincarnation as a cat, or an eternity of nothing - Insert afterlife here.
I'm not placing any bets on who got him, I think that's the point. Death could come from anywhere at any time - In Tony's eyes, everyone is his potential executioner. It doesn't really matter who pulls the trigger - You're dead.
I was really hoping that Tony would make it all the way through without any comeuppance. I would have preferred to see it end with him giving Meadow a hug and sitting down for a malt. It seemed too hackneyed to end it with a judgement (death, jail, descent into madness, etc.), but I appreciate how Chase wrapped it up with five seconds of ambiguity rather than a bombastic climax.
For me, Tony died at the end, but the ending is wide-open to other interpretations. The greatest aspect of the cut to black is that everyone is left to fill in the blanks for themselves - To think. No wonder so many people are pissed.