I've been curious about Runequest 6 for a few months now. I never bought Mongoose's Runequest II (now Runequest 5), but about a year ago I acquired a copy of the old Runequest 2nd edition by Chaosium which is an amazing game (and quite innovative for the time). This new edition sounds like it is exactly what I'm looking for.
Intuitive system. Check.
Optimized for an ancient world / sword & sorcery setting (although medieval and later fantasy worlds are still possible). Check.
A number of different magic systems which can be customized for effect. Check.
Gritty and vivid combat. Check.
Social and societal background has an effect on character creation. Check.
Religion and cults. Check.
Social mechanics. Check.
Lots of GM advice on how to make running Runequest better. Check.
Passions and hatreds (similar to Pendragon). Check.
And if you'd like a look at the book you can check out Lawrence Whitaker's preview video of what you get.
Check it out: