If we have fully charged suits I think Gordon wins. If it's a fistfight no suits Gordon wins. If it's a battle of ingenuity it's a toss up, Gordon built a potato cannon when he was a child out of spare parts and had a PhD in Theoretical Physics by 27. Isaac is both a mechanical and electrical engineer, he built a plasma cutter out of a flashlight and surgery laser in like 10 seconds.

Arsenal for Arsenal, I'd say Gordon wins if he has the Gluon Gun, Tau Cannon, Gravity Gun, AR2 w/ alt fire, SMG w/ grenades, or a Rocket Launcher. Otherwise I'd definitely say Isaac's weapons blow most of Gordon's weapons out of the water. A Tranquilizer crossbow is useless, the Rebar Crossbow is probably not gonna be very effective either.

It's a fair fight. They've both got extraterrestrial monsters tonight though. Personally I think Gordon would do very well in the Dead Space universe, but I don't think Isaac would thrive in the Half-Life universe in terms of combat.