Wow. It DOES look a lot better than the PS3 version—in particular, the player models look fantastic by comparison. I don't regret getting it for PS3, but I'll definitely be double-dipping for the PS4 as well.
I believe word is you'll be able to import your PS3 save, lemmie double check... Yep: "One last treat for current fans of Diablo III on PS3: you’ll be able to fully transfer your characters to the PS4 version when it comes out. Be aware, though, that this is a one-way transfer. Once your level 60 Demon Hunter is migrated to Diablo III on PS4, given the amount of gameplay elements and scenarios introduced in the next-gen version, there’s no going back! Not that you’d want to go back, after seeing it on PS4."-source-
Beautiful. I've been playing it with my wife (same screen co-op is *awesome* and I know she would have been sad/frustrated to lose our progress in the switch.