Using Pathfinder or 3.5E Dungeons and Dragons, I'm very fond of the
E6 variant. We ran a game for about 9 months using 3.5 rules in late 2008, I ran a spellthief, another guy played a soulknife, and a third a cleric, and later on my girlfriend joined as a warmage. While we never even started the planned progression past 6th level, by taking high level play and all of the nonsense it brings out of the equation, it lead to startlingly epic play with a comparably low power level. I never thought I'd take a 5th level character through hell and survive, but we managed to get out before the devil knew we were there...
It's probably my favorite D&D variant I've yet had the pleasure of trying, in ten years of 3.X variants, and I would imagine that Pathfinder would only improve the E6 style of play. You may be thinking that D&D might not be for you, but give it a shot.
If you're looking for a dark setting, try and see if you can track down a copy of
Midnight. I don't have a ton of knowledge about the system, but the three or so sessions we played in it were pretty cool, and it was recommended to me as the best 'world gone fucked' setting on the market a few years ago.