I’ve not played RQ6, but played RQ3 back in the day (and before picking ShadowRun back up was playing in Glorantha, but with the very un-crunchy HeroQuest rules set). So I can’t give you an exact comparison, but maybe have some ideas I can give you.
For the most part, SR doesn’t try to be very simulationist. If you are wearing an armoured vest, it will probably reduce the damage you take, you don’t worry in particular about where you are hit. Damage is likewise abstracted – you have ten or so boxes of stun damage you can take and the same for physical, and every three boxes of damage on either track gives you more of a penalty on your actions.
It does provide some degree of crunch in having weapons with various ratings for accuracy, damage, armour penetration, and for firearms firing mode, type and size of magazine or equivalent, and accumulated recoil penalty as you fire more. There is also a lot of choice of cyberwear (for those that use it), magical powers (for adepts), spells (for magicians), programs (for deckers and riggers) and general gear, all of which has its own associated stuff. It is, after all, in part a science fiction game and in part a fantasy game, so of course it needs to provide cool gear, augments, and magic. For the most part none of this is too hard to handle, IMO, anymore than in older versions of RQ you fussed about which spirit magic you had and whether you wanted the extra encumbrance of chain mail on your legs.
Where SR gets a lot of its complexity is in its conflict resolution system, which is very different than RQ (or most other RPGs, for that matter). The standard test you roll is a skill plus an attribute plus modifiers worth of d6, then you count how many rolled a 5 or 6, and you have that many successes. Depending on the roll you might simply need to achieve some defined number of successes (‘to spot the bullet in the tree takes at least three successes’), or you may be rolling against an opponent and need to roll more successes than them (‘to spot the hidden assassin, you have to beat her successes, from agility 5 + sneaking 4 = 9 dice to roll’). Your dice may get modified by poor lighting, magic, or cyberwear (‘I set my image recognition to look for something like a bullet hole, it has a rating 2 so that adds two dice to my perception roll for this’ – but doing that wouldn’t help you spot the assassin, in fact it might penalize it). The assassin’s dice could be modified by magic (perhaps their agility has been boosted, giving them more dice) or gear (maybe they have fancy active camouflage, like seen in the “Predator” movies.).
And on top of that there are limits. If you are shooting a cheap ‘Saturday Night Special’ hold-out pistol, you can’t count more than four successes on your attack roll, no matter how many you rolled – it just isn’t that accurate so all your skill only does so much good. (and on top of all of that, there is a chance to glitch if you roll an excessive number of ones on your dice)
It is an impressively interesting system, providing a lot of dynamism and surprise, while still giving a reasonable feel to contests. But it does mean rolling, and counting, a lot of dice, which makes the mechanical part of resolving conflict slower than in a lot of systems, IMO.
