Only thing missing from making this a full-fledged bingo hall is the quiet murmur of old people...
A real "number goes up" kind of game. It's really simple yet just as addicting as any incremental game usually is. Add in the ability to save your game and slap it on the app store and you've got a great mobile game (or fun little background game on desktop).
I haven't really got anything to complain about here - this is just a solid game all round. Well done!