bf4 (on pc) is the only game that really feels next gen to me, because of massively destructible environments. the graphical difference between ac4 on pc/ps4 and ps3/360 were really minor, same for thief. Yes, you can definitely spot the difference but its in jaggies (AA) and stuff like smoke and fire effects, the character models and buildings and stuff were at best 1.5x better, and I'd expect an order of magnitude better between generations.
To me really next gen means either the graphics are instantly, noticeably better (like jumping to Crysis 2 from Quake) and/or you get rid of some of the bullshit that 10 year old consoles impose, like tons of loading screens, non seamless worlds, fewer NPCs, bad NPC AI, etc - technical limitations.
I'm really hoping Watch Dogs is a seamless world with great graphics but I'm not too optimistic given its ported back and started development years ago. either way gonna play on PC though, unless the initial reviews are bad.