The first time I played Birthdays the Beginning, I didn't put the controller back down for four hours. I was in a trance, totally incapable of wrestling free. The next few nights went similarly: multi-hour sessions cut short not by dwindling interest, but by the pesky need to get at least some sleep.
I can't say I didn't see this coming. Birthdays is a sandbox title and those tend to have a powerful time-warp effect on me. This specific one also happens to be something of a dream game -- an ecosystem simulator in which your almighty meddling causes species to rise, fall, and evolve.
It might not be flashy, exciting, or much to look at, but Birthdays is such an engrossing game.