I loved this finale for many of the reasons others hated it -- because it took the central concept of the series, the opening repeated before every single episode, and essentially turned it on its head.
Everything we were told about the series each week ("[Sam] had an accident, and woke up in 1973") was wrong. The "real" Sam did not (literally) wake up in 1973. He was a fictional person who woke up in a fictional world. He never needed to work out "the reason" -- he was there because that was his reality.
And oh, how the show brilliantly turned around the idea of "getting home." It kept telling us that Sam needed to get home. Yet, "home" as we knew it for Sam was nothing but a series of voices in the static and strange phone calls. Nothing real or emotional or tangible.
Indeed, the show spent 16 episodes showing us how "1973" was Sam's reality -- "1973," and not "home" was bright and loud and beautiful, and full of characters we loved. The idea that Sam would have to "destroy" (actually kill) these characters-- these *people*-- in order to get back to voices in static and strange phone calls seems almost unthinkable. And yet, he does -- voluntarily or not, he leaves those characters and the world he, and by extension, we, have come to love and goes "home."
The trouble is it's not "home" to him, not anymore. It's not his reality anymore. One of the reasons I can't accept the idea that Sam never actually woke up from the coma is it negates the power of the ending. Sam has to be awake, and "alive" in 2007 to realize he's *not* alive ("You know when you're alive, because you can feel it.") And in order to feel alive again, he has to be...well...dead.
That powerful sequence on the rooftop is wonderful, because Sam finally has all the information -- he's awakened from his coma, and is now "home" -- and yet, he goes "back" anyway. Whereas "1973" was a place where he felt trapped before -- now, it's a conscious choice. How else to explain him *running* to the ledge and *leaping* over it? He's going home. No wonder the BAFTA audience applauded after he jumped.
Sam's decision is further cemented in the closing moments of the finale -- where, for the first time in the entire series' run, he "changes the channel" to tune out the voices in the static. He's spent 16 episodes begging the people from 2007 to talk to him through the radio, phone and television. And now, he no longer needs them. It's not his world anymore.
I guess the finale really worked, because for me, "Life on Mars" wasn't about Gene Hunt or Annie or the politically incorrect policing procedures and politics of the '70s. It was the story of Sam Tyler, trying to get back to 2007 from "1973." He worked out the reason, and he went home.
Exactly as the show promised. :)