There are actually some great zm maps, it's just that no one ever plays zm anymore.

Panic beach, beachstrike, tx_highschool, urban downtown, onadega, etc.

Those are just off the top of my head. What might help, though, is to take a day or two and go through every single map on the server and ask the people online if they want to keep it or remove it. It might be difficult, but I think it's necessary for the health of the zm server.

On top of that, there should be some restriction for replaying maps over and over again (i.e. sorrento/shroom, there a few others).

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To add to the overplayed list, Mountain Escape and Paranoid.