Thought I'd chime in with a few impressions:
The game looks GREAT. It appears a lot of work was put into the game looking more detailed, the environments more lush, and everything more colorful. The characters also look a bit more detailed, with the swap characters being particularly neat. Only drawback of all this is that it's sometimes a bit more difficult to find breakable crates on the ground than it was before.
Most of the characters I've played with so far are pretty good, only exception being Slobber Tooth, who not only seems completely generic but fairly useless. I haven't tinkered that much with the swapping feature, but the few times I have I've noticed that it does actually change quite a bit what I can do with the character. The way upgrading works for the swap characters is that you can spend money on upgrades for the upper half and lower half of the character, and those are tied specifically to that half. Nice way to smooth out the upgrade purchase process.
The game is pretty easy so far, and they've made adjustments to make it easier, such as giving both players life when food is eaten, and a lifebar that seems like it doesn't deplete too much. We've only played two levels so far, but if it doesn't ratchet up the difficulty soon, I'm afraid I might find myself a bit disinterested in it.
I won't delve into story much, as to not spoil it for anyone, but it's more of the saturday morning cartoon fare. Light, enjoyable, and approachable.
I do notice an increase in load time for switching characters, which is frustrating given that's a big feature of the game. Not enough to ruin the experience, but it is a minor complaint of mine.