We have certainly been very pleased (and a little surprised ) by the number of not only orders, but re-orders, which are a good demonstration of demand. If things carry on like this, I think we might be looking at the second best selling RPG of the year (after D&D, natch). . .
Just to throw in something specific here, I like the new "action" and "reaction" mechanic. The strike ranks from previous versions worked, but this seems to be a good way to not only clarify and streamline that mechanic, but to also include some interesting tactical decisionmaking in the process.
For instance, the fact that you must burn a reaction to riposte is very nice. The player must then decide whether it is worth an extra attack to give up a block or parry. That's the sort of game mechanic that makes RPG combat fun: noncomplex, quick choices which have real tactical value in both directions.
Better yet, under the open license, I can see the "action" and "reaction" mechanics being a really nice hook to hang new game rules off of. For instance, certain monsters may have special abilities that can be used as a reaction.
I agree with the simplicity aspect...it took me just fifteen minutes to generate a character...gotta love that! Combat is fast and deadly...just like in real life. You have to think before you fight...the polar opposite of D&D (oh, I have 200 HP's...I can slay that army of orcs by myself!). Sure, heroic gaming like that has it's place, but for my money you get much better roleplaying from gamers with a potentially deadly, gritty combat system.
Also the spell system. Simple and elegant, classic BRP-type stuff. I love the fact that they've keep percentages for magic spells. In my mind, magic should never be so dependable as to not call for a roll and should also be challenging (for the character) to cast, demanding a skill score.
Also also, I'm personally not a huge fan of feats and such, they can be fun but often become the only defining aspect of a character for some players (which may say more about class and level systems, but hey...). Feats also become a bother to keep up with at higher levels. Sure, they're are Legendary Abilities in RQ, which I like BECAUSE they are legendary...you have to wait a while to get them and not every Joe Mercenary has them. Plus, they're expensive...I can see most players blowing through Hero Points before they buy those.
There's more but I've taken enough space...gotta go work on my first scenario!
The speed and simplicity are nice while still managing to create a satisfying gaming experience. Look at combat, for example - simple ways are built in to make it more than two people taking turns hitting each other. Without cumbersome details, the combat system rewards dynamic action.
The rest of the book is of the same spirit - just the right level of detail to be highly playable. Ultimately, from character creation to combat to rune magic, the way "RuneQuest" plays just feels right.
The disease rules have changed. The one thing I disliked about RQ2 and 3 was the characteristic-blasting disease rules which I always imagined hadn't been thought out at all - someone had just gone, "I know - diseases reduce your attributes!"
It's also a bit harder to get your arm chopped off. I thought it was too easy to lop off limbs in RQ2/3 especially if not much armour was worn.