I think you are looking at the season all wrong. Granted I thought the finale and the climax were great but I guess I could see how someone might feel differently.I got the point it was 1977, can you get to the climax of the season already? Oh... that's your climax.... sheesh.... it's like dating someone for a while only to see them naked for the first time and you are disgusted by them.)
I think the difference between Season four and season five of Lost is that season four was designed as a self-contained season with an endpoint. I'm looking at season 5 and season 6 as one big season the way BSG's season four was split up. So I could see that the writers were introducing the last pieces and characters so season five was mostly setting everything up for the last half and now with that out of the way they can start answering everything that hasn't been addressed. This finale was more like a regular episode and I suspect if in a year or two you go back and watch season five and season straight through it'll play that way. It wasn't about an endpoint as just another link in the narrative chain with the endpoint being the series finale. It's not so much a 17 episode season as the first 17 episodes of a 34 or so episode season.