huge spoilers ahead!
ok, so the idea that sam would be forced to choose between 1973 and 2006 was unsurprising, especially given the trailers. and frankly, the coma thing was well signposted and introducing a new idea in the last episode would have been pulling a rabbit out of the hat: they could go with mad or coma at this late stage. i had one or two novel ideas that they could have gone with, but only put them out there because i hadn't seen anyone else suggest them...
hmm. so, there are still two interpretations, rather cleverly. if we assume 2007 was real, and 1973 was a dream, then we can assume he's back in a coma, or possibly in heaven. (cos there is no way he could have survived that fall...) but then the bright light at the end of the tunnel was working the wrong way?
or, we could assume morgan was right all along. in which case, what exactly were the first 5 minutes of the series, and the intermediate 10 minutes, exactly? we would have to rationalise these as hallucinations or false memories of sam.
in all, a satisfying dramatic conclusion which nontheless leaves the debate about the metaphysics of the situation (read: wtf was going on) open: which is what you'd hope a classic would do, leave you guessing.
i can't say i wouldn't like to see a season 3, but i think with an ongoing mystery show you need to rein in and resolve your mysteries eventually: otherwise you end up like the X-Files. But them I'm very much of the school of thought that reckons rewatching a murder-mystery should make you kick yourself at how obvious it was, rather than noticing how they cheated (M. Night Shyamalan, I'm looking at you...). Ashes to Ashes, if that ever gets made, may be worth watching, but I daresay it won't have the sf and mystery elements.