If you are a Joe fan, you owe it to yourself to give this game a chance. It kinda grows on you.
Granted, this is almost certainly due to the fact that I am a huge geek when it comes to G.I.Joe, but nonetheless...
I really liked that the game is not just a retelling of the storyline in the movie. As I am sure you've already heard, it goes off on its own and reaches into the extended Joe universe for characters and content.
Along those lines, I think they did an excellent job on the designs for the characters in the game that are not portrayed in the movie. Each character retains enough of their classic look to be immediately identifiable but also remains grounded in the universe of the movie. For example, Beachhead has his classic green balaclava and camo pants but dons the same (apparently standard issue) body armor to protect his torso. I think this was a great approach and I wish they had done something similar in the movie.
There are a handful of vehicles featured in the game that were not in the movie. In general, these are designed pretty well and if you played with the toys at all as a kid, then you will immediately recognize the majority of them. My only real complaint regarding the vehicles is that in a couple of cases, the developers simply re-used the same vehicle model with a different color scheme to identify it as either Joe or Cobra owned. I thought that was kind of lame and lazy.
Also, you are teased at the beginning of the game with an image of a wrecked Trouble-Bubble being run over by the tank treads of the Mobile PIT, but sadly you never encounter them in combat during the game.
Not surprisingly, I don't agree with the critics when it comes to the game's voice acting either. I thought that it was generally pretty good and sufficiently cheesy. I mean, this is a G.I.Joe game after all. It probably wouldn't have worked in a more serious game, but it works just fine here.
And what about the horrible controls you've been hearing about? Well, you'll just have to trust me when I say they are not as bad as you have been lead to believe. I think that industry reviewers in general did not spend as much time with this game as they should have in order to give it a proper review. I suspect that this is par for the course when it comes to movie tie-in games.
For example, I have read a number of reviews citing the vehicle sections as being particularly bad due to control scheme issues. However, had these reviewers taken a moment to explore the Options menu, they would have found that they could toggle the vehicle controls such that they behave much like the on-foot controls (which work quite well, in my opinion). I'm not sure why the developers chose to set the Resident Evil-esque controls as default, but at least the option is there to switch.
Also, I read complaints about the targeting system losing track of your chosen enemy if you aren't firing at them constantly. Again, had they explored their controller a bit more or flipped through the game manual, they would have found that the L1 button can be used to lock onto a particular enemy. You will remain locked onto this enemy, whether you are firing or not, until either the enemy is killed or you choose to switch to another target. This mechanic actually works fairly well once you realize it is there.
The co-op is well implemented and is preferred over playing by yourself if you've got the luxury of having a geeky roommate or spouse who is down for kicking Cobra butt.
The bottom line is that this game deserves a bit more credit than it has received. If you are a G.I.Joe fan looking for a reasonably fun romp through the Joe universe, then this game will not disappoint. If you are not a Joe fan, then you can probably skip it. But then again, if you aren't a Joe fan, you probably aren't bothering to read user reviews in the hopes of finding someone like me to tell you that it isn't all bad.