Rating: Better than you expect, if your expectations are very low.
There's a weird vicious circle going on with this movie. Many people have rightly said that, if your expectations aren't too high, this is an entertaining film. But that faint praise has a way of raising one's expectations of the movie, which is not a good thing.
To say that this is a stupid film is almost unnecessary -- if you've seen the trailer, you've heard Dennis Quaid solemnly intone: "This is General Hawk. The mission is a go!"
That said, it may be more instructive to mention that this movie is so stupid that it quite literally has characters in submarines fleeing from sinking ice after an explosion breaks up an ice pack.
As a frenetic popcorn movie made up of almost nothing but battle and chase scenes, it certainly isn't boring, but so much of the film is CGI -- and not very good CGI for the most part -- that it really feels like you're watching a cartoon.
This, of course, takes it back to its source material, which was pretty stupid in itself. The movie derives virtually none of its inspiration from the underrated Marvel Comics title of the 80s, rather paying what little respect it does to the silly cartoon series of the same era.
Even there, though, it is only a superficial nod. None of the character dynamics even from that shallow kids cartoon have survived into this film. Of the cartoon's three principal characters present here, only Duke has any substantial part to play. Scarlett is a sidekick and romantic interest for Ripcord (who, if he had any story outside of the toy line, I don't remember it, yet is here placed in a starring role).
Snake Eyes, the iconic mute ninja/commando of the franchise, is present, but story-less. Other than some flashbacks of his rivalry with evil ninja Storm Shadow, he is a complete cipher. He's not even mute in this version, merely having taken a vow of silence. Everything tragic and mysterious about his character has been completely excised, and that pretty much goes for every other aspect of the franchise as well.
Stephen Sommers clearly understands the G.I. Joe property about as well as he did the classic Universal monsters he co-opted for Van Helsing (i.e. not at all), but at least this time around he's managed to maintain a better momentum, with fewer groan-inducing moments. Some of the action sequences are quite spectacular, particularly one in which the bad guys attempt to dislodge Snake Eyes from atop their vehicle by ... well, you kinda have to see it.
And, honestly, if you don't see it on a big screen, it's almost certainly not worth seeing, because it's a BIG movie.