Star Trek: The Motion Picture - Very much an acquired taste more than a movie that can be enjoyed by the mainstream.
Star Trek II: The Wrath of Khan - Excellent and a cult classic.
Star Trek III: The Search for Spock - An ok movie but nothing special
Star Trek IV: The Voyage Home - A great movie which the mainstream really dug due to a good mix of clever humor and action as well as an environmental theme.
Star Trek V: The Final Frontier - A WTF? movie which just went to the way weird and over the top.
Star Trek VI:The Undiscovered Country - One of my favorites, it showed the Fedaration as a not so 'We are all happy and tolerant' society and it had a good mix of action and political intrigue.
Next Generation Movies
Star Trek: Generations - WTF? Dull and 'out there' plot and a really crappy return and demise of Kirk.
Star Trek: First Contact - Overall a good movie but nothing special but several bad 'dumb down' retcons were made to the Borg and some of the Trek Earth history. It's biggest crime was the introduction of the 'Sexy Borg queen' which made the borg from an unstoppable and inhuman cybernetic force to something laughable as a clear attempt at making them more appealing to the general audience through sex appeal.
Star Trek: Insurrection - Was stupidly crap and barely remember it due to this.
Star Trek: Nemeis - A clear attempt at trying to mainstream the franchise by incorporating ridiculously stupid crap such as 'Picard does donuts with the dune buggy' and overall a lame plot but not as bad as Insurrection.