I played and ran RQ3 close to 3 decades. It was also the first rpg I ever played. I've tried many other rpgs, but I've always preferred RQ. It would take too long to list all the things I enjoyed about it, so to be concise; it's the feel of realism in fantasy. You don't just hit people straight in their hitpoints, and you can parry enemy swordsmen like in swashbuckler movies, and even powerful characters still feel like humans instead of superheroes. A RQ character is more like Zorro or Indiana Jones compared to the Supermanlike D&D characters.
And in addition to the great rules, RQ was coupled with Glorantha, which is an unsurpassed fantasy world.