Define your expectations for running "ok". I have it installed on my 4s and I'm not having program crashes or problems with using the phone or text. I did not upgrade immediately from 7.1 to 8.0X, but waited for 8.1.. When I first updated I could not get the SMS handoff feature to work between my phone and my MP laptop, which is less than a year old. There was a thread about people having a problem with this feature, and I tried all of the fixes people suggested. None of them worked. 2 days later I noticed that I could see both iMessages and SMS text messages on my laptop. I have no idea why it started working. This has been the only "feature" problem I've had.
I have had no problems with my music,and I do use itunes match, but being in a 3G system I don't often stream videos. Camera seems to work fine. I don't play games on my phone, so I can't speak to that.
The system is not as fast as it was when new. I don't find it terribly slow, but others probably do. The 4s was the last 32 bit system, and there are probably hoops that both Apple and app developers have to jump through to make a 32 bit system run what was designed as a 64 bit OS.
