Funny, but I actually watched Star Trek: The Motion Picture over the weekend. I had forgotten how much I really like that film.
It certainly does not get the universal praise that films like The Wrath of Khan get, and it definitely had its problems. But I actually like the slower pace of that film, emphasizing the mystery and bringing in more true science fiction elements. Star Trek as a television franchise has always been willing to go in a variety of different directions and tell all different kinds of stories. But as a film franchise, somewhere along the way they fell into the "every film has to be an action/adventure space opera" mold, and I think that's to its detriment.