I will never understand critics (and gamers) who say a PS3 game looks like a PS2 game. Sure, it's possible, but it just doesn't happen. Even the worst looking PS3 titles look leagues ahead of what was possible on the PS2.
If you need more proof of this simple concept, check out this new video from PlayStationAccess. In it, they take a look at the evolution of in-game visuals from the original PlayStation all the way up to the PlayStation 4. Some examples include titles like Crash Bandicoot begetting Knack or Disruptor begetting Killzone: Shadow Fall.
In short, PlayStation 4 games are going to look good. They may not live up to some gamers' impossibly high standards, but they will look better than PS3 games.
Aside from the obvious graphical leap, the PlayStation 4 will offer many unique features that were impossible on its predecessor. The big one is a built-in DVR that records your gameplay for later sharing via social media. It also features an improved online experience and more sophisticated AR gameplay through the new PlayStation Eye camera.