I forked up the $20 for a PDF of HeroQuest Glorantha last week, and I'm very glad I did.
First off, this is the HQ rules specifically tuned to Glorantha. Secondly, I think of it as a version 2.5 of the rules. Many bugs have been squashed, and there are new, better ways to do things. Though some of those ways would change game balance a lot, so we'll discuss before we adopt them.