I've been playing a lot of Zombieville USA lately. It's somewhere between a beat 'em up and a Contra clone, depending on how you play it. It made me notice that onscreen directional controls work a lot better when it's just left and right, like it is in this game, than it does when they use all 4 directions, or full 360 degree analog.
I will say this for iPhone controls, though: I was playing Pac Man Championship Edition on my iPhone and getting a bit frustrated by it, which I thought was due to the controls, but when I went and played it on my 360 with physical controls I was getting consistently worse scores.