Soosiz is the best I've found. Giana Sisters is decent, but very very old school, and not very challenging. Assassin's Creed 2 is sort of like a side-scrolling platformer, sort of like Assassin's Creed mixed with Sonic the Hedgehog. It's a great game and definitely worth a look, check out some videos.
I really liked the Plushed trial game, so take from that what you will. Soosiz is amazing, as someone else already brought up. Recently I got done playing Alice in Wonderland and that is up there with my favorite platformers on any system. I seriously love that game It's short, but it's very very sweet. The puzzles aren't all that difficult usually, but they're very fun to play around with. So Alice in Wonderland is short, but I honestly believe it's worth it.
ok, here's my list of played platformers good: soosiz. this was just perfect. no complaints (ok, maybe one or two nicks but i loved it) gravity might be a bit weird at first, but you get used to it and grow to love it giana sisters- pretty little platformer, closest you'll get to mario. it takes a while to get hard, but is still pretty fun play assassins creed two- super fast paced platformer with slight combat elements. problem is, unlike sonic, the levels throw enemies and jumps at extremely unoportune times (sometimes) so it can feel like the game wasn't designed to go so fast. i still had a blast though! dislike: castle of magic. i played part of the game, but never really caught onto it. it felt easy and shallow and didnt really feel 'alive' to me. for the 99 cents i got it at i guess it was ok, but nothing more. plushed. the game is just boring to me, since you can't kill the enemies by jumping on them. that's pretty much my main gripe.
Go to the upcoming forums and look for the metroid/megaman inspired game. Look at the screen shots, watch one of the old videos, and then wait for it to come out.
Ya I tried the lite version. The main thing I like about it is the level editor but other than that it's OK.
If you have a higher-end device, get Assassin's Creed 2. It's the best side-scroller I've played, but it's EXTREMELY laggy if you don't have a higher-end device.
Both Rolandos are great, but they're more puzzle platformers. If you want a more action-based game, get Soosiz. Castle of Magic is decent, and Bounce On 2 looks good. (it's on my list of games to buy).
Soosiz and Hoggy are the best in my opinion. Especially Hoggy... very underrated but extremely clever, fun, and challenging (especially as you get further in). My two cents!
Soosiz is good, but I'd definitely recommend Rolando 2. While it isn't really a traditional platformer, the controls work perfectly on an iPhone and it's still my favorite game on the device.