All right, @G-Man. Here is my list, which certainly isn't original:
1. Too stalemate-prone, due to density, build restrictions, Switzerland.
2. Ven-Tri adjacency.
3. "Automatic" moves (A Con-Bul, and to a slightly lesser extent, F StP(sc)-Bot.
I have additional quibbles regarding the naming of certain provinces, but those are very minor.
But improving the game by creating better maps has always been one of the main motivators behind variant creation, and this has led, indirectly, to the creation of this platform and to this very discussion.