The number one reason I love Avatar so much (among a long list of reasons) is the brilliance of the writing. The plots are full of twists and very deep, the episodes are not formulaic, and the characters are round and colorful. For such a standard, 'Jet' was by far too predictable. As soon as the plot-triggering deus ex machina took place, I knew how the story would unfold. That's a bad thing.
Jet will seem nice, be admired by all but one of the protagonists, then turn out to not be so nice at all, with a healthy dose of disappointment for all those who trusted him. Fill in the details, and voilÃ , you have an episode.
Also, as soon as Jet appears on stage, he starts hitting on Katara. I found his stumble at the end of the fight just to stand in front of her (way too close, really) pretty silly. Katara of course is almost immediately infatuated by Jet. It's strange that Aang doesn't feel jealous or so, unless he's also infatuated by him. But let's not go there.
Jet seems pretty charismatic, and I kept hoping throughout the episode that the writers will give me some great twist, to make Jet good, and not to follow through with this oh so predictable plot. Fat chance, though.
Indeed, Sokka witnesses a paranoid Jet assault an old man, then we find out that Jet plans to liberate a town by destroying it with both it's Fire Nation oppressors and its Earth Kingdom populace. Katara and Aang remain blissfully unaware until the last moment.
There are two things that save this episode from a worse grade. Jet's fight with Aang (not to mention his cool sword-catchers), where a non-bender pretty much successfully faces off against the Avatar, and the only plot twist, at the end.
I could have expected the dam blowing up, but I had high hopes that Aang and Katara would save the day using waterbending. These hopes were smashed, in a good way. The town actually gets flooded, and the standard little girl's puppet is seen floating on the water. It's a nice twist to the climax, which, after the generic build-up, redeems this episode somewhat.
Overall, it's an average episode with a a solid ending. It doesn't do the show complete justice, but it didn't fail miserably, either.