Much like the original game, the entire expansion The Following is playable in 2-4 player co-op. If we've learned anything from pop culture zombie survival (The Walking Dead, Left 4 Dead, etc.) it's that strength comes in numbers.
You're far less likely to become overrun when playing with a partner. You can watch each others' backs and divvy up the approaching horde - not to mention the buggy capabilities with partners. One player can drive while the other shoots, or two players can take separate buggies and work together to crush the zombie army.