4>1>2>3>5 for me, although 1 over 2 is probably coloured somewhat by nostalgia. Civ 1 and 2 were brilliant for their time, but a little naive... rational or genre-savvy players can crack them wide open. Civilization 3 wasn't much less exploity, and given the heavy-handed attempts to "fix" degenerate playstyles it felt clumsy, bureaucratic and artificial to me. Civ4 struck a very good balance: wildly different approaches are viable, degenerate playstyles are possible but tricky enough to set up that "playing fair" remains a legitimate option. Civ5 is plagued by similar problems as Civ3... the underlying game is fragile, and the makers needed to bend over backwards to keep it from falling apart. Amusingly, the less I like a Civ game overall, the more I like the graphics... didn't care for IV's cartoony style at all.