One big thing is that you can't change the default browser, so any time you click a link you end up on safari. In my experience (I tried iPhone for 2 weeks after my previous phone died, before returning it and switching back to Android) that makes installing a different browser effectively useless.

The rendering engine restriction is less obvious to the average user. And, frankly, if you don't trust Apple with your data then what are you doing using their network stack?