User interface frequently locks up, or partly locks up, meaning you can move the map, but can't tap on any tiles. Also, there's a severe issue with server communications, I assume, where frequently you will clear a bunch of tiles, and then it will generate an error message and all your work will be lost. It makes the game frustrating at best. It really needs to be fixed. It could be a good game, but right now it's almost unplayable.