I've said it before, few of the ST:OS films hold up as well as The Motion Picture (yeah, I said it). Wrath of Khan is the best, most entertaining of the bunch, but The Motion Picture is the series of films' truest attempt at science fiction. I give it a heartfelt second position. It's also easily the one with the most 'epic' feel (many of the others felt like big-budget tv shows--which is why, I think, they are beloved by true Star Trek fans), with 'The Undiscovered Country' close on its heels.
Of course, I also stand by Tron and Lynch's Dune as very misunderstood but qualifiable masterpieces, each in their own right/means--and they like The Motion Picture are popularly derided.
As for 'Enterprise', I think it's way better than most people gave/give it credit. Some of the cast members couldn't emote their way out of a paper bag (Ensign Mayweather, anyone? I'm sure he's a hellova nice guy, but...) and some of the writing was weak, but overall it was pretty good. If they would have kept The finale was indeed horrible, second only to the finale for X-Files in wasted potential and let-down factor.
As for the new prequel movie, I have one nervous wish--that they don't go all "Beverly Hills 90210" on us. The problem w/ most American TV/film today is the utter lack of interesting faces, i.e. real characters/character actors. Everyone looks the same, in that plastic good-looking generic L.A. way. Boooriiing! Granted they had Kirk and mod-headed Chekhov and all the 'babes', but they need some real grit and unique faces to round out the crew--today we'd have no angular Spock or gaunt older Bones, they'd be buff lookalikes.
They should also consider the best casting choice of recent Star Trek, Jeffrey Combs, as either a villian or a major role--now he's a great character actor!