(personally, I like the director's cut of Motion Picture, but it's not at all the rest of the series, nor is it available on blu-ray, which is theatrical only). They took it from the attempt at a big budget version of the TV series that was Motion Picture, and turned it into a kind of Horatio Hornblower meets Das Boot nautical adventure in space. II was directed by Nicholas Meyer, who is mostly famous for his Star Trek work, and his Sherlock Holmes pastiche novels (Time After Time is great too).
Nimoy took over and directed III and IV (Meyer returned to do script work on IV), which along with II form a trilogy within the series, where each movie is a direct sequel to the last. IV is a much light-hearted film with a ridiculous sounding premise, but actually works really well on its own merits.
V (direct by Shatner) ties up a loose end from IV in the beginning but is otherwise a wholly unrelated and unwatchable film, and can be easily missed.
VI should have been included in that set you mention, but people seem to like trilogies so for some reason it was left out. In the same way that character motivations in III are strongly based on events in II, character motivations and major plot points in VI are based around the events of III. It also serves as a wrap up to the original crew series as a whole. Nicholas Meyer directs again, and I think it's a pretty damned brilliant piece of work that never gets mentioned amongst the best entries in the series.
Generations - Felt like they resurrected two corpses for the sake of continuing the franchise. Kirk, who had been sent of extremely well in VI, and the entire Next Generation crew, which had a fantastic series finale not too long before, one that did not beg continuation. Felt really pointless, until...
First Contact - Which is all sorts of good. I suppose if suffering through Generations was the price of getting First Contact, then it was worth it.
Insurrection - Really long, not terribly impressive episode of the TV series.
Nemesis - Really long, not terribly impressive clip show episode of the TV series. Seriously, large portions of this movie feel like they were cherry picked from people's favorite episodes and re-purposed as a movie plot. Not offensively bad, but the writing was on the wall, and when you consider the next Trek movie we got, it was, like Generations, worth it