Imagine you play Canabalt, the prototypical one button jump game. Now imagine playing that game at the same time as everyone who is playing it at that moment. You've just imagined Edmus, and it's awesome.
It reminded me of Super Meat Boy - that moment when you finish a level and watch every single one of your previous attempt simultaneously, watching them all die, one by one, until your only successful run jumps to its conclusion. Edmus elicits that same pleasure, but a weird sense of community, like a childhood race to the school cafeteria. There's a strange satisfaction as you watch those you're playing against drop by the wayside, as you power on.
It's such a simple game, such a simple concept. But so innovative.