Some people say stock ICS makes the phone feel A LOT smoother while others say it only makes a minor difference...
As for me, with stock gingerbread 2.3.6 the phone feels smooth enough (if I don't use a live wallpaper) but the overall experience in responsiveness is way behind iOS and my old iphone 4. Especially most of 3rd party apps completely lack animations compared to iOS, like the facebook app for example. Unnecessary effects you'd say but do make the interaction with your device more pleasant.
And another thing, stay away from the Samsung built-in email client and use the gmail one instead. It's laggy as hell. When I try to simply select and delete a mere message, the phone and the tactile feedback become almost unresponsive.
I wouldn't go back to Apple but to be fair, healthy criticism (based on facts and extensive usage) for every product should be acceptable. Nothing is perfect.