One sure sign of a great videogame is if you turn off your console, but still feel as if you're living inside the virtual world you've been exploring. And after 10 minutes free-running across the crumbling rooftops of ancient Venice in Assassin's Creed II, every ledge, windowsill and drainpipe you see in the real world will become a potential handhold to help you perilously scuttle up walls like a chimpanzee. 4/5