Warner Bros. has released a trailer showing the visual difference between Batman: Arkham Asylum and Batman: Arkham City on the PS3 and the PS4. Watch the trailer and decide for yourself what looks better. To me, I think the backgrounds are improved, but the character models tend to look better on PS3 in several cases. Pay close attention to Joker especially.

Batman: Return to Arkham - cover

It becomes increasingly clear, in my eyes at least, why this game was delayed by three months.