I am currently working on a big Capture the Flag TDM. The game is played on a large, desert-like map. Players must mine minerals for their team, and then bring them back to the team refining station for cash. Bigger minerals will be found by going deeper underground, but the risk will be greater because the caves are filled with places for enemies to hide. Once the minerals are brought back to the base, the money can then be spent on turrets, vehicles, or bigger guns. You can even buy structures like bunkers or towers and upgrade them to be larger.
I am still working on this project, and I hope to release it when it's finished. I feel that the upgrading and mining mechanics, along with a capture the flag gamemode, will help encourage teamwork between players. Even people who are inexperienced with first-person shooters could impact the battle in a meaningful way by mining minerals, transporting troops, and defending the base to help form the backbone of the team.
Also, I would someday like to host a speedkart gamemode that incorporates elements from the Mario Kart games, with power ups, more customizable karts, and booster pads.