The plot, essentially, is that this sentient planet/robot is tooling around the universe eating other planets (didn't Douglas Adams write a Doctor Who episode about that once?). He/it/whatever wants the Autobots out of the way, so he enlists (well, enslaves) the help of the Decepticons. Etc., etc., etc. The good guys win, the bad guys die, Rosebud is the sled, Bruce Willis is dead, she was killed by her father while he was being inhabited by Bob, and Keyser Sose is guy he was talking to and I was in the turkey all along.
The movie doesn't really have a lot of problems, other than that the action starts right away, and never really lets up. This would be fine if there were more plot to support it, but there isn't because they spend so much time shoehorning unnecessary characters into the story to please the fans (who (by the way) probably had a median age of seven at the time). Reduced to a handful of essential characters Transformers might have been a good popcorn flick, but there just wasn't room for plot between the cameos and explosions. Incidentally, I think the most impressive thing about the movie is its casting: Eric Idle, Casey Kasem, John Moschitta Jr., Leonard Nimoy, Robert Stack, Judd Nelson, Orson Welles (in his final role) and the ubiquitous Frank Welker. I can only imagine what moral sacrifices were required to secure that ensemble.
Another interesting facet of the film is that it uses a lot of visual action movie conventions which didn't pop up in Hollywood until the early to mid '90s. I've never heard anybody refer to Transformers: The Movie as groundbreaking in any stylistic sense, but director Nelson Shin deserves points for that stuff.
I'm somewhat weirded out by the subject matter, which deals with slavery and agonizing torture (it's a movie for kids, after all). Optimus Prime (leader of the good guys (that's the Autobots if you're playing at home)) dies during the first third of the movie. Bambi's mom gets shot too, I think. Oh, well.
Anyway, it's worth sitting through if you've ever thought it sounded interesting, but I didn't need to see it. What's the big deal? Am I missing something here? The fact that I'd never seen Transformers: The Movie has always been shocking to my friends. Then again, the people who gave me the hardest time about it are former roommates who make an annual pilgrimage to BotCon. Maybe my social group is excessively comprised of hardcore Transformers fans.
On a semi-related topic, the friends who told me I should see Transformers also talked up G.I. Joe: The Movie. As a kid I hated G.I. Joe, but they got me seriously interested in in it more recently. After Transformers, I'm not so sure I even care.