Well I like my 4S, but the camera is poor. The 5S will have a better camera, but it's not going to be as good as the Z1s. I'll be quite happy to sacrifice the convenience of ecosystem compatibility in order to have a better product.
I've no real issue with the 4S camera, however that's probably because I have a couple DSLRs.
There's no larger screen
People need to get over the fact that the overall phone dimensions aren't going to change on the 'S' model (or the 'C' model!)