iOS5 (on a 4S) is the first time I've ever been unhappy with my iPhone. Apps most definitely crash way too often. I don't know if it's the OS or badly programmed iOS5 updates, either way, it shouldn't happen on an iPhone.
And to add to that, the 5.0.1 update has left me with a ridiculously fast draining battery (I managed to fix the battery problems in 5 but no such fixes work in 5.0.1) and constant SIM Failure messages.
No good Apple.