I'll agree the graphics look a bit hazy at distances -- that's probably the worst thing about the game from a purely aesthetic point of view -- but to say they look "PS2" is just mean.
In terms of gameplay, it's certainly no worse than previous games.
Assassin's Creed was a good game when it first came out, but
Assassin's Creed II made you realise how mundane and repetitive it was.
Brotherhood was also good, but if there was any game in the series that felt like a quick cash grab, it would have to be
Revelations. That isn't to say
Revelations was a terrible game, but it didn't add enough to be enjoyable - I literally had to force myself to finish
Revelations; I just didn't find it engaging in slightest (not to mention I wasn't a fan of the setting). But with
Assassin's Creed III, I'm enjoying the settings, the gameplay tweaks (to things like free-running and combat, despite it being insultingly easy now), and the new mechanics (both combat and environmental). Overall it's a solid game.