Overlord’s resurrection as a co-op action RPG is probably not the most exciting of comebacks. We already have quite a few of them and not very much of whatever you want to call the original games’ strange brand of evil Pikmin shenanigans. That's why it's a spin-off rather than Overlord 3, I suppose.
A new trailer offers very little in the way of details, but it briefly touches on the co-op and single-player aspects. Very briefly. You can muck around with three evil chums, working together or screwing each other over with traps, or you can play on your own. And that about sums it up!
Overlord: Fellowship of Evil is due out this year.