Former S4 owner here. I miss my V8, but not the problems that came with it. Styling is subjective, but my S4 had CF front and rear spoilers, CF interior and nice Recaro seats.
Overall impressions vs my humble 328i Sport is that the S4 feels heavier. It's also a beast on the freeway at high speeds. Interior is on par, again that is subjective...
Ultimately it was the poor lease terms that turned me off. I have owned my past 2 cars and returning to lease for a short period to save some $$$. Residual on the S4 is pretty bad. I also just wanted to try something new. The new S4 bodystyle is nice, but the F30 really caught my eye. Even the base model trim F30, IMO looks better than the S4. Looks aside, handling is much more enjoyable in a 3... still miss that V8 though...