Runequest is NOT a new game by any means. Mongoose has done another version of it. D100 is called basic roleplaying. It has been around for years.
D100 to me is a lot simpler. the game itself is a lot simpler than D20 games. It is CLASSLESS and LEVELLESS...
Glornatha is the published world for Runequest, but they are doing others like Slaine, Lanhkmar (already out).
With d100 you are not as limited to things. For instance, in D&D you have two types of magic that of Wizards and that of clerics. Each follows the same principles. The classes vary!!!
Runequest has several types of magic: SOrcery, Rune, Spirit, Divine, Dragon, Folk, and more to come...
Each has its differences and similarities, but it would be hard pressed to put them into d20 terms.
Like D&D, however, skills are plenty. They also have a version of feats called "Legendary Abilities". These are gained through Hero Points.
GLorantha is a unique and intruiging world setting, I have never bought or saw on that matched it...
Do not limit yourself to the D20 Frame of mind, expand your horizons...
GET RUNEQUEST, you just MAY LIKE IT....