RuneQuest in its most recent incarnations has been published by Mongoose and now The Design Mechanism. What this has led to is three publishers coming out for material all with a closely related source. What this tends to do is product a lot of material that can be easily folded into you existing/new campaign. This reminds me of AD&D in the early and mid 80's where you had Arduin, Mayfair and several others producing material. You end up with small run products that can give your game a distinct feel, think All the worlds monsters.
I am currently working through the new version of Mongooses runequest, which they have re branded as the game Legend. BRP from Chaosium is in the mail and I am waiting for new on The Design Mechanism's RuneQuest 6. I plan on working up some of the differences and flavors of each system.
I can already tell you runequest and Legend have the cult based magic system that comes from Runequest. There was something I read about a spell less magic system that allowed for something like Shadowrun's physical adepts in the RuneQuest 6. This is nice as I have felt the game does much with magic but the combat systems was a little bland for warrior. This could be because of the gritty nature of combat.
The system or systems are pretty exciting to me as they seem to allow for many different characters, and allow for you to explore facets of your character without leaving a class. In pathfinder I feel like my cleric must level to gain more healing power or the party will suffer. I am playing a cleric because the party would suffer without one. I might prefer something else but I am trying to be supporting of the game rather than disruptive.