So Zombie Risk works pretty darn good
as outlined. We played a 4 player game using those rules and it was noticeably more fun fighting the zombies and attacking each other via proxy than simply fighting each other directly. There were suitable amounts of hatred for other players, but it was a little less personal. There were many more moments of cooperation and rooting for other players than you would get in a typical game. It was fun to use familiar game mechanics in a new way to quell the growing zombie hordes.
The infection on a 1 mechanic was really good and a lot of fights took a sudden turn for the worse when a player's units converted to zombie units mid fight. It was also good that the infection cards only dropped two units into countries as this limited the attack dice at first and made these skirmishes more tolerable, but made it all the more dramatic when it happened that fallen armies were infected. The game started out a bit slow and at first the zombies seemed to be a bit weak and it was a concern that players wouldn't be able to get their cards each turn for lack of targets. However as the zombies gained new units after each player turn, and also the 'infection' cards caused outbreaks and conversions of player countries, it soon became apparent that these zombies were getting to be a real problem. Slowly the zombie faction spread and soon there were heroic fights just to knock the zombies down a country or two to prevent them from getting that one extra reinforcement next turn. By the time that players are turning in card sets for higher numbers of units, the zombies had very large hordes in place to counter. There was a real sense of survival horror and fighting against growing hordes that came with these mechanics.
There was a lot of option for strategic manoeuvring and for player diplomacy, and since everyone had vested interest in the zombie faction it was a much more interactive game than I remember regular risk being. I am sure that a strategic co-operation in the early game would make it pretty easy to wipe out the zombie faction, but the player self interest in controlling territory seems to be a decent counter to that. It is good that the zombies only receive one attack per turn and then the two infection cards as it prevents them from being used too aggressively against a single opponent or for a signal purpose.
The players suggested that it would only be fair to have some sort of 'cure' mechanic where zombie forces that rolled 1 on a loss would turn into humans again. I am not sure this is a good idea but it was a popular request all through the game. I suggested that perhaps if the zombies lost on a 1 against a roll of 6 the zombie could be cured - making it a more rare occurrence. I would consider this as a house rule of the house rules I guess.
Some clarifications/qualifications to the rules:
1. Setup should be done by dealing out all the country cards (minus the wild cards) and putting units on the countries you receive - at least for the zombie faction if not for all players. I assumed this since it's always how we played, but it's not in the official rules I had. Once all territories have a unit, then the remaining units are placed as reinforcements in player order. Players should take turns to place a number of reinforcements equal to the number of players and then place a zombie unit until they are all deployed.
2. Zombies get reinforcements for the number of countries they control but do not get cards or continent bonuses.