Most people didn't like Sum of All Fears either, and while I wasn't too much for the reinvention of the character of "Jack Ryan", Afleck did a pretty decent job there too.
TOS Movies
1) Wrath of Khan
2) Voyage Home
3) Undiscovered Country
4) The Final Frontier
5) The Search for Spock
6)The Motion Picture
Next Gen
1) First Contact
2) Nemesis
3) Generations
4) Insurrection
My fav's although Generations could be considered Both I guess... I would rate it Behind Undiscovered Country in the TOS list...
The one thing about Star Trek III is that while it's not great, it's an intergral watch because of the death of Kirk's son...
BTW, bestbuy has had all the star trek movies for 9.99 for a while now, so anyone who needs a title or two to round out the collection, go to the store and see if they've got it (Doubtful) or get it off the website...I hope the HD-DVD and Blu-ray versions don't come in god-awful packaging like the DVD's did...
Watching ROTS last night made me want to put together a dvd with just light saber action... Might put one together of just the battlescenes from the Trek movies...