So ... I interpret this question as 'if there were a video game world with real world rules/laws of physics except for the ones we would have to change to allow for a zombie attack, how would you handle the situation?'
There is a helpful video from the folks at CommonCraft called "Zombies in Plain English" -- it's a light-hearted explanation of how to deal with a zombie attack. I think it could be useful to you: http://www.commoncraft.com/zombies
My own counter-zombie strategies are usually non-violent, and would probably be boring in a video game. Basically, I'd treat their condition as a progressive illness; if unable to cure it, I'd try to distract, convert, or otherwise manipulate the zombies into doing stuff other than eating my brain, etc., until I could escape the dangerous zone. As a back-up strategy, I'd recruit non-zombified people to assist with the plan ("hey, why don't you go out there and check to see what's up?")
If different zombies represent different types of games, it's likely there will be different ways to defeat them. You have to grind your way up, do side quests, and get enough points in your skill tree to defeat the RPG zombie. There's going to be a ninja-y zombie you have to stealth up on to defeat. There will be a zombie you can just blow up (you'll know him 'cause he will stand next to barrels of explosive fuel). There will be a zombie you can assassinate from distance using a realistic sniper rifle (proving, perhaps, the lone gunman theory is plausible). There will be a zombie who organizes a terror cell - he's really hard to find, but he keeps occasionally releasing video or audio tape of himself instructing his forces to eat your brain (one way to deal with this guy is to go to war with some country he ain't in). And there will be a zombie who makes you solve puzzles (that are either too easy, too hard, or make you go d'oh!) to defeat him. Why don't you go out there and look for these zombies (got to catch them all, y'know) while I stay here in the lab working ...
There is a zombie survival thread at http://www.escapistmagazine.com/forums/read/18.56182 -- you can read about various approaches there. I like the "go to Canadian Tire" strategy. In the US, you might try Walmart or maybe Home Depot. Gather the items you need to implement your strategy - guns, ammo, chain-saws, duct tape. Meanwhile, I will be in the lab working on the anti-zombie cure, recruiting other zombie fodder, or developing zombie behavioral conditioning techniques... maybe I can train them to walk over cliffs at the sound of a bell.
If the game uses real world physics, some items, like a chainsaw or sawed-off shotgun, may not behave as you expect. Be careful to experiment on less-menacing zomboids before expecting to tank in and take 'em all with whatever you think looks cool. If chainsaws were such great weapons, they'd be standard issue in the military or commonly employed by terrorists. They're really great if you want to have a weapon that jams up a lot, commonly injures you more than your opponent, and just isn't meant to be used that way.