Better battery life than the 4s for one. My mom who had the 4 (on the latest OS) just switched to a 4s and she says the battery life is significantly less. My dad who just got a 4s (but had a dumbphone before that so wasn't sure how much was him not used to the difference) was constantly complaining about battery going down even when it was idle. Hell, longer battery life would be awesome!
Makes me kinda glad I still have my 4.
Also, cheaper storage price (or I suppose more storage cause if they put more in most likely they'll get rid of the 16 GB and make the others on the cheaper level).
I'm hedging on NFC payments (recently heard that the CC protections you get if some one steals your credit card may not apply to NFC, or they may insist you put a pin on your lock screen. I wouldn't mind if there was a pin to get into the payments, but I don't want to have to unlock my phone every time solely cause if it gets stolen I won't get the CC protections you'd get with a CC. I'll just keep using my credit cards instead, it's not that big a deal).
Faster processor (of course. And it will since the 4s already has a faster processor, so I doubt they'll go to a slower one than the 4s nevermind my 4)
I want those 3d maps they were rumoring about a few months ago (Apple bought out some company)

.
Other than that, I'm not picky, everything else (including the maps I mentioned) is gravy (though I'm not sure I want a bigger screen, I like the portability of my phone and I'm not sure I want 4G connectivity cause I suspect AT&T will use it to force me off my unlimited plan if I want an iphone 5).