Could tower defence be the ultimate "it's Friday and I am here in body only" genre? I haven't really thought about it before, but Rift Riff's effusively laidback crowd control has me pondering those optimal moments in any tower defender when the incoming horde hits the flamer-MG triangle just right, and you can settle back comfortably into the role of clockwatcher.
Rift Riff encourages this behaviour by being nice to look at. Created by a trio of developers including Hidden Folks designer Adriaan de Jongh, it's a world of spacey, sun-carved mountains, forests and monoliths. The towers resemble the sacred architecture of Monument Valley, and the colour scheme and general ambience remind me of Cocoon. There's a demo, if you fancy it.