Yikes, this trade signals the end of a really bad misevaluation by the Seahawks FO. Granted, Harvin was probably the MVP of this past SB, so any evaluation of his time in Seattle has to prominently feature that, but for what they gave up in draft picks and the amount of money that they gave this is just really bad. The one area where they were really smart, though, is in only guaranteeing him $14M. Vs., say, the $30M that the Dolphins guaranteed to Mike Wallace right around the same time.
I hated the original Vikings trade for Seattle when it was made, and how it panned out was pretty much why. For all the things that Harvin does well, he just doesn't score that much. The Seahawks never really figured out how to get him the ball, because he's not a great WR and is too fragile to play RB. He's good for a significant injury and a couple of wow plays per season. As badly as it worked out for the Seahawks, though, I think it was still smart to trade him while he has value, get some meaningful draft capital in return, and free up some cap space for Wilson's upcoming extension.
All of that said, I understand why the Jets made the deal. His high base salaries mean that they'll still be paying him a lot of money in base salary, but they have a ton of cap space and no one to use it on anyone. I wouldn't go so far as to say that I think this is a good trade for them, but if he sucks they can cut him, and they need to put weapons around Geno to figure out if he's their QB or not. He now has Harvin, Kerley and Decker at WR, Amaro and Cumberland at TE, and Ivory and CJ at RB. If he can't produce with that lineup and a decent line in front of him, then there's no excuses left to be made: he just sucks.