Alexander loves the FP ones, too. HE likes to slam his wet hands on the screen (they're always in his mouth in between activities) so I have to help him since wet hands on an iPad are pretty useless. I actually don't find them too annoying either, which is an added bonus.
We also have the Wheels on the Bus for iPad which is nowhere near as interactive. We both got bored quick. I wish the Seasme Street ones were free.