I have never successfully run or played a session of Aftermath. I've tried twice, both a long time ago, and it just bogged down in character creation and a sample combat. I know there have to be a few people out there who have run it, but it quickly runs into the hassle factor wall and eventually the cry goes up - "Couldn't we just play D&D?"
Runner up is the other system of which I have never successfully run a session:
I know people have run it and played it, I used to know some personally, but it just never clicked with me. Between D&D, Runequest, GURPS, Palladium Fantasy, and Fantasy Hero (and continuing on with Pendragon, Savage Worlds, and 13th Age) I just never found a reason to play Rolemaster over any of those options. I'm not slamming it - if you like it and play it then thumbs up from me - but it never worked for me as a player or as a DM.
- People tend to think of Champions as complicated and it can be, and I own a lot of stuff for it, but my friends never complained about it being complicated. Once you grasp a few basic assumptions about the system (3d6 roll low. 5 points = 1d6 of effect, Stun/Body/PD/ED) then it seems pretty intuitive to me. I'd say that certain other games are at least as complicated as Champions, including ...
- Pathfinder is about as complicated as any other game out there once you start throwing numbers on top of a die roll. So.Many.Things can affect every single roll that it can be very challenging for a DM to keep track of everything. It's presented pretty well, and the basic system has been out for so long that many people don't even think about it any more, but it is not a simple system in play.