I agree. I don't think that TMP is a good movie, but it has a scale and a scope that the others don't.TMP is the only film from the first 10 films that actually feels like a big budget movie.
Yes. That's its biggest problem, IMO. It's trying to be 2001 instead of TOS.It's also a very different animal than the 60's TV show. It's aim was closer to 2001: A Space Odyssey than TOS.
Someone put together a "modern trailer" for The Motion Picture and it's awesome.

I agree. TMP is, at best, an interesting failure.It's interesting in the ways it's flawed.
Yes. One of my big problems with TMP is that both Kirk and Spock are nigh-unrecognizable versions of the characters we saw on TOS. Kirk is grumpy, stressed, humorless, and territorial, and Spock is in heavier denial of his emotions than he ever was on TOS. They don't have same dynamic or any of the back and forth they had with McCoy on the series, and after ten years, the filmmakers should've tried to give us at least a little of that, even in a story that was largely about the characters regaining the dynamic they had in TOS. McCoy is still recognizably himself in TMP, but he just doesn't have anyone to bounce off of anymore. That's perfectly illustrated by the scene (scenes?) where McCoy just walks onto the bridge, says nothing, and walks off again a couple of minutes later.One of the central reasons TWOK saved the franchise was its return to the soul and heart of its main characters' interaction and challenges through difficult / dark times, much like the best of TOS.
Yes, TWOK is much more of a shoot-'em-up than TMP was, but the reason audiences responded to it more positively is because they got the Kirk/Spock/McCoy dynamic absolutely right. We've got a scene of McCoy calling Kirk out on his shit ("Dammit, Jim, what the hell's the matter with you?"), some great Spock & McCoy snipes ("Jim... Be careful." / "WE will!" / eyebrow raise), and a couple of touching Kirk and Spock scenes. The character interactions are perfect.