It's actually a pretty decent game, or rather, collection of mini-games. The problem is, it's not quite worth the trouble of loading it up and having to travel the world (map) to get to whatever you feel like playing. Also, I wouldn't pay full price for it, but yeah, there's worse things you can spend $10 on.
Topic - Of the spin-offs I've played, my vote goes to XD... it just feels like a crappy version of Colosseum (and even that wasn't all that great TBH) with a boring and linear story.
EDIT: Just remembered that I had a Pocket Pikachu back in the day. Good lord that thing was awful... like a crappy tamagotchi where you could only ever get 1 type of animal. About the only redeeming feature was the mystery gift trade feature with G/S/C, and even then you had to grind that little sucker like crazy before you got anything of value. if that counts as a spin-off, then it's by far the worst (that I've experienced anyway).
Another day successfully wasted. "I need a new quote for this signature." - Me