Runequest was a major innovation in a time when TSR's Dungeons & Dragons game ruled the fantasy gaming market. It had a classless system (everything worked off skills), a coherent and interesting world, Glorantha, that had no hobbits or halflings, allowed players to run monsters as well as heroes, a body-part based combat system, magick available to all players and over all, a sense of humor that was evident through the books.
Glorantha avoided the usual melange of fantasy races which was a refreshing change from the Tolkein-heavy D&D mythos. They had, among others, Dragon-Newts, dryads, and duck-men, and a coherant, consistent mythos worked out for all of the races. The game produced a number of supplements expanding on this world, the most memorable being Troll-Ball, a new type of fantasy football where the ball was a live newtling doing his or her best to get away from the teams.
Later on, much of the game's mechanics would transfer over to another of Chaosium's more successful games, Call of Cthulhu, which was a roleplaying game based on the works of H.P. Lovecraft set in the 1920s, most memorable for its insistence on sanity points, which players would watch trickle away over the course of a campaign until they were reduced to mewling, gibbering husks of their former selves.