The basic line (B/X, BECMI, Rules Cyclopedia) editions remain ever so popular. In fact, the game I'm running at the moment—Conquering the Barbarian Altanis—is using the lightly house-rule version of B/X edition.
I'm sure I've played some obscure RPGs that I've forgotten by now... On day six I wrote about a RPG/TBS game series Romance of the Three Kingdoms. Back in the day no one in my circle ever heard about the game (except from me). The same would go for Vandal Hearts II.
The treasure was where they left it—a pile so wide six men could easily roll in it. Everybody but Amanda, Silente, and Theo dove straight into the pile, stuffing their sacks with as much coin as they can. A pile of mangled deer corpses next to it were no concern of theirs.
“Ahem—Boys!” Amanda coughed loudly, pointing down the dark corridor they haven't ventured through yet.
A massive human-like head, adorned by long, greasy, lanky hair—imagine armpit hair half-a-meter long—with horse-like jaw hovered high in the air. Its diabolical cackle revealed a sickening array of ghastly, yellow, rotting teeth. True horror was revealed only after it'd made few more steps forward.
Lantern light now fully illuminating the figure, revealing its elephant-like body covered in warts and blisters. To further the nightmare, ten more heads like the first one—with varying degrees of balding—were connected with thick worm-like veiny tubes to the body.
It has to be Silent Hill! I played horror games before, but never did I turn off the console out of fear... Man, that first scene when you stumble around the mist engulfed city and then wander into that dead-end alleyway when dead flayed babies assault you... Fuck that shit.
Adventurer Conqueror King System Imperial Imprint, a second edition of ACKS which massively updates the rules, will be coming to Kickstarter this year. It consists of three books: Revised Rules, Judges Journal, and Monster Manual. Each is a wealth of information on its own, but together they are simply mindblowing. Even better, Judges Journal and Monster Manual will be great for all OSR judges, even if they don't run ACKS.
The simplest RPG I'm playing at the moment is Basic / Expert D&D. It was made for kids. The most complex would be the first edition of AD&D (MM, PHB, DMG, UA). The complexity mostly comes from disorganised and sometimes incomplete rules. But it is a wonderful game nonetheless.
I'm a simple guy. I like well bound, thick hardcovers. Smyth-sewn when possible. If they are impractical to wield, that's only a bonus. Judges Guild Deluxe Collector's Editions are hard to beat when it comes to those criteria.