It's got a larger battery... that alone will make me look closely at it.
As far as how it looks, I don't really care. I put my 3GS in a rubbery case, where it's lived since the day that I bought it... which defeats the whole put of sexy designs... if I bought this new one, it would go in some rubbery case too (I ebay them, I'm obsessive about scratches) and however it looked, it wouldn't matter.
The front facing camera seems neat but it seems like a bit of a gimmick. But it could be neat to make video calls... maybe. I think it would be weird to make a call while holding the phone out in front of me like some Star Trek tricorder. But I'll keep an open mind until I see it in action.
The higher res screen would be nice... I wonder how they'll do apps when they have another size screen to deal with... interpolate the existing apps to make them fit?
The flash will be nice... taking photos without it indoors with a 3GS requires everyone to stand really still.
But at the end of the the only major gripe that I have with my iPhone is the battery. Anything they do to make the battery last longer (like make it bigger) would probably have me filing in for an upgrade some time this summer.
One thing that's odd... Apple signed the agreement with the EU on the new cell phone charging standard. Where's it's microUSB charging plug slot?
http://news.cnet.com/8301-1035_3-10274953-94.html