I really enjoyed TMP the first time I watched it. It's a really tough one to re-watch though (for me), mainly because of the lengthy ride through v'ger as someone else mentioned.
The TMP uniforms do look dated. As someone else mentioned, they are the 1970s view of futuristic...which is now a retro view of futuristic. I'm sure at the time they were awesome.
The dark red uniforms that followed, on the other hand, hold up very well. Instead of trying to be futuristic, they're trying to be militaristic. I know Gene Roddenberry didn't like that direction, but to me it really worked well as a "look," regardless of the inspiration or the implied meaning Nicholas Meyer was going for. It's more unified and just worked better on film in my opinion.