This one is going to be tough. Nevertheless I intend to take a good old crack at it, because I am forced to admit that I have a serious soft spot for this movie. I can't remember when exactly I first watched it, but probably somewhere around 1989 or so, definitely after I first watched Wrath of Khan; though I was young enough that the two probably didn't register in my mind as being part of the same franchise – certainly the films have a very different look and feel about them.
I'll start with the elephant in the room and then fight my way back up from it. The Motion Picture is boring. It is part of the received fanbase wisdom, and for once there is a significant amount of truth to it. Paramount took a look at the success of films such as Star Wars and Close Encounters, and decided to make a film harkening back to 2001. Half an hour could certainly have been cut from this movie without affecting the plot significantly at all; the director admitted that a lot of the effects sequences were just dropped into the movie whole without proper trimming – not his fault, he didn't have the time before the studio-imposed release date. The film is slow, it drags, and there are an awful lot of shots of actors looking out of the screen in amazement.
And yet...and yet...those effects shots are all worth the price of admission by themselves. (Heck, if there's one Star Trek movie you are going to buy on Blu-Ray, it really needs to be this one.) That shot of Admiral Kirk flying towards the refitted Enterprise for the first time is a love letter to the most iconic spaceship in movie or television history. Perfectly executed, perfectly shot, and Shatner does his job magnificently well. (We're at what in my opinion is the height of his acting career here – Treks I through III. We'll get to 'why I think Star Trek III is the best Star Trek movie' soon.) The shot when the ship leaves Spacedock, also great. These were technical triumphs in their day, but that's not what makes them great. What makes them work is that they look real, that the shots are well chosen, perfectly poised, and perfectly paced. (Someone needs to do an 'effects only' version of this movie.)
The actors...well, mixed here. I'm going to focus on four here – not that I don't have a high regard for the other ones, but Takei, Koenig, Doohan, Nichols et al don't really get anything much to do but sit at their consoles. Understandable, if unfortunate – there is only so much time on screen. (Read Chekov's Enterprise if you want a picture of what this movie was like from the trenches. Hell, read it anyway, it's a good book, and Koenig's work is worth the price of admission.)
Taking them in order – we'd best start with Shatner, I suppose. He's got a rather thankless role here for the first half of the movie at least, because he is portraying a Kirk whose love for the Enterprise is that of a stalker for his target. Frankly, it's downright scary at times, and it really doesn't synch in with Kirk's usual attitude. Yes, he wants command, he revels in it, and it bitterly regrets giving it up – but this is too far. Fortunately, by about the middle of the movie – after the rather contrived 'asteroid in the wormhole' moment, this is pretty much forgotten and we're back to business as usual, which is Kirk as Commander. His biggest role in the plot is over by this point, and he can concentrate on a good, solid performance.
Thank Christ Nimoy agreed to come back. Originally he wasn't going to make the movie; if he hadn't, we'd have been in serious trouble, because he is bringing the humanity to the piece. Never mind that he is playing an alien, he gives the connection with the V'Ger probe that the rest of the movie sorely lacks; that this was a Shatner/Nimoy-conceived moment is somehow not surprising. His transformation from uber-Vulcan to taking the best from both sides of his heritage, and accepting that his humanity is an important part of him is perhaps a little rushed, but that's an artifice of this being in a movie rather than a show. (Imagine if Phase II had happened, and this had been a season-long character arc. That would have been worth watching.)
DeForest Kelley was always a good, solid actor, and here he has a very important job; he has to play the straight man to both Shatner and Nimoy. He has to be the one to bring Shatner back down to Earth and end Kirk's slightly psychopathic desire for command, and he has to support Spock's role as well. Usually Star Trek focuses on two relationships: Kirk/Spock and Spock/McCoy, and this is definitely truest of the movies. In this one I would argue that it is really Kirk/McCoy – something that we saw far more in the series than we did in the movies – that comes to the fore.
Finally – Stephen Collins, Commander Decker. We're all aware that this is Riker Mark I, and what is missing is, well, character. He accedes to Kirk's command of the Enterprise with only mild petulance, essentially shrugging his shoulders and getting on with his job, and faced with the loss of the love of his life, Dea...Ilia, again, there just isn't much in the way of emotion there. I suppose what I'm going to say is...that this is really a non-character. I suspect the script just didn't give him that much to work with, and faced with Kirk in full 'MY SHIP, MINE!!!' mode, he was always going to have problems. A script that should feature him doesn't, largely because he isn't one of the key characters of the series. He's a guest star, and not who the fans have come here to see. (Want something bigger – give the 'Decker' role, lost love and all, to one of the supporting characters. Give it to Sulu, or Chekov, or Scotty. Even if it means losing that character at the end of the movie, it would have given it a hell of a lot more drama and a great end for that character that we would actually care about.)
I have a feeling that I'm going to be doing all the Star Trek movies at some point, aren't I. Which probably means rewatching Nemesis. So, that being the case, lets start some sort of ranking. Given that I have only done a single one at this point, the current scoring is pretty obvious:
1: Star Trek I