Solid Snake vs James Bond. If Bond could find Snake, he might have a chance.
Alexander the Great's army vs Gaius Julius Caesar's army. I think The Romans would have the edge of the Macedonians. Despite Alexander's leadership, the Romans would only have to outflank the Macedonians. They also beat a Macedonian army (under a King Phillip) at Cynoscephalae. Alexander's tactical genius would be the biggest advantage teh Macedonian army had, but I am not sure if it would be enough.
Master Chief vs Doom Guy. Both space marines fighting monsters in green power armor (Doom guy is more of a man though, he isn't fully encased and has a white helmet) with soem realistic weapons and some over the top laser weapons. It would be a tough fight. Chief can only carry 2 weapons at a time while Doom Guy can carry as much as he wants. Doom Guy also has the BFG9000. At long ranges, the Chief might have the edge because of his snipers. Medium is a close matchup. Close range goes to Doom Guy because of the Super Shotgun over a regular one. Melee is also close, chainsaw vs energy sword is a close match-up. In the end though, I have to give the Doom Guy the overall edge because he kills more of more kinds of goons (Halo only has 5 or so, Doom has well over 20 varieties and on harder difficulties they are in very large numbers) and the bosses in the Doom games are much more vicious.
Kratos vs Dante and Dante. 1 is a rip-off, the other a white haired punk in a red trechcoat.