MrSeb writes: "An Italian researcher with a penchant for retro games — or perhaps just looking for an excuse to play games in the name of science! — has used computational complexity theory to decide, once and for all, just how hard video games are. In a truly epic undertaking, Giovanni Viglietta of the University of Pisa has worked out the theoretical difficulty of 13 old games, including Pac-Man, Doom, Lemmings, Prince of Persia, and Boulder Dash. Pac-Man, with its traversal of space, is NP-hard. Doom, on the other hand, is PSPACE-hard."