RuneQuestII or RQII was one of the first RPG I bought rather than using my elder brother's copy, though it was preceded by Metamorphosis Alpha, Bunnies & Burrows and Flash Gordon and the Warriors of Mongo.
As it broke away from the D&Disms like levels and classes it was intriguing mechanically and far more comprehensive than early versions of D&D and the other really strong factor was the background of Glorantha.
The mechanics using the D100 or percentile rolls for success became the Basic Roleplaying System (BRP) that Chaosium used for other games including Call of Cthulhu. The BRP system works pretty well, but like any other ruleset has its limitations, which are mainly that it focused mechanically on low level skills and character attributes in common with most of the other early RPG. Advancement in skills by successful use or practice is a mechanism that I prefer to the level based 'okay I killed a dozen orcs so suddenly I'm better at opening locks' from D&D.
Magic in RQII is more pervasive than some settings, but the common battle magic is quite limited in its effects and the powerful Rune Magic takes a long time to be available to a character and requiring membership of a cult. The cults in RQ are a better approach to depicting religion in game in my opinion than the default options in D&D, with this helping to integrate the rules into the gameworld with the choice of cults and their associated gods.
Dragon Pass and the other areas in Gerentela were the usual settings for the game with this area of the world of Glorantha having also been used as the basis of the board game that was released as White Bear and Red Moon and later rereleased as Dragon Pass. As a setting it contains many common fantasy tropes, but with distinctly different takes on them. The Aldramyi (Elves) are actually plant folk rather than generic humanoids, Trolls have a mix of types and are more interesting than in many games, the Dragonnewts are a complex race related to the dragons that give Dragon Pass its name and there are no 'orcs' as such.
The races of RQ include the much maligned Ducks, who I always felt gave an interesting edge to the game being a race under an ancient curse that could be played straight or for comic relief. Personally I tended to play the ducks fairly straight though at times with a temper resembling that of Donald Duck.
This is a game that I'm really keen on playing again as it brings back good memories and I feel that mechanically it still holds up quite well in comparison to more recent games like 3rd Edition Dungeons & Dragons or Warhammer FRP. I prefered this edition to the later Avalon Hill produced RQ3 as it is fundamentally the same mechanisms, without the sorcery rules for magic which I don't regard as a loss. Most importantly though RQ3 lacks the Gloranthan setting which to me is a major loss as that is one of the critical things in the games appeal.