I've been revisiting the movies recently as well, mostly the Blu-Ray theatrical versions. For the most part, I prefer the versions I saw and enjoyed in the theater. None of the expanded versions did anything substantially positive to the originals - except for TMP. After months of rewatching the BD theatrical cut, I decided to pop in the Director's Cut re-edit.
Like any re-edit and restoration of a Star Trek work, complete with new effects, people either loved it or hated it. I loved it. This isn’t the thread to go into a detailed critique, and it's been done before anyway. But let me say that I enjoyed both versions. Each has flaws, but in all, they are the same story. Yes, it's a slow movie. This was the 70's, and super fast paced SF films didn't take hold yet. Star Wars was still an anomaly. Alien, Close Encounters, The Black Hole, were all deliberately paced. TMP was working just fine until the two (count 'em, two) V'Ger flyovers in a row. At about 5 minutes apiece, you're talking a ten minute look at special effects which, honestly, aren't worthy of that much awe. They don't move the plot along, there's almost no dialog, and they just grind the film to a halt. You could compress them into a two minute sequence and still have the scale of V'ger established. Since we never learn what most of that stuff is we're looking at, it's pointless. The only thing that works in those scenes is Jerry Goldsmith's score.
The only long effects sequence I feel was justified was the slow flight around Enterprise in drydock. In context, it makes sense and even as a kid in the theater, I enjoyed it. It had been 10 years without new footage of the old girl, and we were taking this tour with Kirk. So, that was fine. Other, long establishing shots of space stations (Epsilon 9 and the orbit station) could have been trimmed, since nobody really cared about random space stations. Now, if you discount those shots and the two V'Ger flyovers, then you have a film that's not all that slow. It's not an action adventure, it's not meant to be. It's a journey of discovery. Whether or not it succeeds is not the point. If we don't go in expecting an action piece, then this is a fine film. Many of the original episodes were dramatic rather than action packed. TMP is as valid an "episode" as any of them.
I enjoy the film and revisit it regularly. It is also the only Trek movie to take place in this particular era, during the presumed "second five year mission." The uniforms, which succeed and fail at the same time (great use of TV era rank braids, not to crazy about seeing Decker's Dick, the stirrups were funny, but I liked the Admiral uniform and Kirk's short sleeved shirt), are never seen again. The rec room was amazing and I wish we had more scenes in there. Really, it's the only Trek film to feel like and honest to God movie. It feels epic, thanks to Robert Wise. Could have done with out the funky blurry lenses though. I forget what they're called, but they keep the subject in focus, but blur around them. Very odd.