What is the most under rated gamemode?

Personally I don't touch too many gamemodes, So I'm interested in what other have to say, what gamemode is never played but you think people would love.

Maybe not underratted, but not so much popular as it was - Flood.

Bunny Hop - I have spent about 4K hours on it. It has a lot of potential, and is actually really fun when you get the hang of it