Conceptually, I don't really consider "experiments" as maps. It's only a map if it's a fully fleshed out idea that I intend for others to play.
So on the FPS front, of projects that I can actually remember, I've left three unfinished. One was a map for Reaction Quake 3, one was a Portal map, and one is arena_beacon, which I can't complete due to utter disinterest in the arena game mode.
Don't ask me about non-map related projects. My record there is... less impressive. :\