I'm addicted to a simple, fun roguelike called Meritous.
The rooms appear to be generated fractally. On my current game there are 3000 of them. Part of the fun is going room to room and watching the larger pattern appear on the map.
It's not quite a one-button game but it's close. You move with arrow keys. When you hold down the spacebar you generate a psychic charge - when you let go the charge radiates in a circle from you.
The charge will destroy enemies and their projectiles. You go room to room, destroy enemies with your psychic charge and collect psi crystals.
Those crystals are used to upgrade your shield and charge.
The game is largely about movement and timing, dodging shots in order to build up a more powerful charge. Some enemies will only be destroyed by a powerful blast of psi power.
You'll be surprised at the depth to the system. I think it's genius that extra functionality is contained inside objects - the upgrade machines, teleports, save points. The primary verbs never change, you don't have to worry about anything but the core gameplay and proper assessment of your enemies.
Give it a try. Even the graphics are a delight.