I am not entirely certain that what I want to say belongs here, but maybe we can figure that out as we go along.
I have played Dungeons & Dragons for longer than I have been an adult, so when a friend convinced me to try World of Darkness, I was dubious but willing. It turns out that I liked the game, and hated the rule systems; what I did like about the systems, however, was that it used only one kind of die, the d10. The problem for me was that successes (i.e. roll an 8/9/10 to succeed, harder tasks require more successes) felt arbitrary. Also significant: I liked that it allowed for opposed rolls (i.e. you roll to attack me and I roll to dodge your attack), which were new to me in an RPG.
D&D could easily operate off a success system - but then there would have to be a success range for each die, which would be silly. Instead it uses modifiers (base attack, skill bonuses, armor class, etcetera).
Digging through one of my 'old RPG' drawers, I found a little gem: Michael T. Desing's Army Ants. I suppose that someone else must know about this game, since I own the second edition - and that means there must have been some demand for the first. Anyway, what surprised me was that in my new state of mind (RPGs don't need lots of dice! They just suck without them!) I realized something that I thought was fantastic: AA does not use successes, but it does use one kind of dice (vastly superior to WoD's d10 dependence: d6's! You can buy them in blocks!). Even better, it used opposed rolls to determine the success or failure of an attack (or skill check, or whatever). I am not about to claim it as the perfect RPG (not by a long shot!) but it was still an enjoyable concept and an enjoyable system, happily merged.
To get to my point: I was wondering if anyone else had any similar experiences or similarly 'simple' RPGs to share. I do not want to exclude 'board game' RPGs, but I am mostly curious about persistent pencil & paper games that are, for whatever reason, easy to learn or play. I ask my question in this way because the 'fluff' of a game is usually the easiest part to work with, whereas the system is the part that needs to be checked, learned, memorized, relearned and rechecked.