I found that RQIII was somewhat more "pedantic" mechanically speaking. I have to keep referring to the crit/impale/fumble table, which is becoming a chore for aging eyes. I put it in my Kindle with larger type. In a recent character sheet redesign, I added spots for those special numbers to reduce the load on players. I understand the more precise nature of it, but question the need. RQII you just had to remember your times tables, ala fives and twenties. In spite of that, I generally liked and preferred RQIII, and its pedantic approach, as I went to it exclusively and even heavily incorporated its sorcery system in my own non-Gloranthan campaign setting.
This is just as well as I found much of the early RQIII Glorantha supplements to be slapdash in nature. I thought "Gods of Glorantha", in particular, tried to do too much and none of it well. I was either not interested in many of the cults, or I was interested and found them lacking in details. I'm looking forward to Chaosium's redux of that one and long form cult write ups. No doubt it will have to have Kyger Litor too....;)
I found the chargen system in RQIII to make fairly anemic characters. By the time they could deal with a few trollkin, as starting out adventurers, they were already 'one foot in the grave' old. I frequently had to tweak them a great deal to get them to where they could hang on a bit in the game. Sometimes even tossing the chargen rules aside entirely. This is particularly evident with sorcerers who I thought gave up too much physical prowess for a poor exchange of magic.