Kameo is far more of a platformer than a "Zelda-clone."
In fact, it flat out is a platformer, with a little more fighting than perhaps your average platformer.
The only real similarities between Kameo and Zelda are that the majority of the fighting takes place in designated "areas" though if it were a Zedla clone it would have puzzles that are required to be solved before moving along... instead it has platforming using the various elemental warriors - not many real puzzles at all.
When you say "sidequests" numbering over 40 I have to laugh. People really overstate this term. You do sidequests in Final Fantasy, not in Kameo. Buying a elemental fruit from a vendor is NOT a sidequest (or finding it somewhere really really obvious that the game leads you straight to). There are some exploration rewards in the game, to be sure, but nothing that is a "sidequest." There are also (a few, very short) mini-games, which are also not sidequests.
You can go back and play the levels for a better score to unlock new stuff, though most of it is so trivial that I fail to see why I would ever try to get it all done, outside just wanting to have it all done and receiving no rewal in-game reward for doing so. I would call this feature an "extra" though, and a badly needed one... I went through the main game in 10:13 on my first playthrough, and I took my time. There just isn't that much to do in a single playthrough. This is a disturbing trend in just about all genres of gaming, and I expect it to continue, but that doesn't excuse the fact that Kameo is far too short.