Zombie mini game would be awesome!
But I think so as long as it is an actual party game like Uther Party (I'm assuming it is), just based on a zombie invasion.
Now noting this, I have some ideas for your existing mini games, and some new ones.
First - you should have Classic Mode, in which players try to individually win points and Team Mode, which is the players versus each other in two teams.
1. Defend the house
Make this simple, with a small house (enough room to move around) and like four or five entrances. Although, you should make it strategy based. Like, being able to lay a certain amount of explosive barrels.
2. Road Rage (vehicle mission)
This sounds pretty awesome. Everybody has buggies, driving through zombies. Normally, you should have to avoid zombies in a medium area, hitting them will kill you. But, you should make it so if you use the Rage ability, you will kill zombies you hit.
3. Escape the Forest
Make this with the survivors separated, in a dark forest where you can only see in a very short range. You have 3 speed boosts, and 1 flare. Your attack can take down a few zombies, but you can easily be overwhelmed. This is all about survival.
4. Kill the Infected Marine
You should make this in a courtyard with walls. The attacks will be shot in a line, so you can dodges them. Its everybody versus a giant, mutated overpowered zombie marine (In the Classic Mode I suggested earlier, maybe somebody could be the infected marine).
5. Hunt down the mad scientist
I got nothing on this one - I personally don't like it.
6. Protect the miners
In Classic Mode everybody should have their own miners to protect. In Team Mode, teams should have a group of miners to protect. You are on walls overlooking your "quarry" where your miners work, and your shooting down zombies.
Now my ideas...
Zombie Trappin'
You and the other marines are in the middle of a collapsed mine. Soon the zombies will come for you, but luckily the miners had mines and an assortment of traps, and each marine has a number of traps. You are supposed to dig through the area, lay traps behind you find new ones, and just survive.
Mow Em' Down
You and the marines are behind barricades with artillery. All the artillery is lined up, and when you activate one (by pressing "D"), it shoots artillery forward, killing all zombies. For every zombie you kill, you get a point. At the end of a round, or when the zombies kill you, whoever has the most points win.
Kamikaze!
Each marine is a ticking time bomb - at any second they will explode. They are in an arena full of zombies. If you are attacked by zombies, you will blow up. You have two abilities - Cut a Cord and Electromagnetic Shield. Cut a Cord will reduce the amount of time you have 'til the explosion by three seconds. Electromagnetic Shield will make you invincible for 5 seconds, but if your time bomb goes off while it's up, nothing happens, you just die. When you blow up, every zombie you blow up counts as a point for you. When everybody is dead, whoever has the most points wins.
the Undead Labyrinth
The Undead Labyrinth is a giant pacman-like dungeon. You actually move like pac-man (you are constantly moving, and left and right turns you). The only difference is - instead of 5 ghosts, there are hundreds of zombies attacking you. There are also no points to get, but there is Rage, which will make you mow through zombies.
That's it for now.