Hehe, I'll do my best to explain. I'll start with the FF books, as you brought them up as a reference. With the Fighting Fantasy books, I don't know about you, but the combat never really gripped me. The storytelling and puzzles were great, but the combat was dull. It wouldn't take long (particularly if my character died) to just cheat and ignore the combat.
DQ is the opposite of that. Not that storytelling and puzzles are not important also, but people will replay DQ because (primarily) of the combat and hero system.
In DQ you complete quests by defeating monsters. When you defeat a monster you get rewards (think Diablo, think Warcraft, think Dungeon Siege etc). You can choose one reward (sometimes more than one) to equip your hero. So right there, you are making choices about your hero... each reward will boost certain attributes and/or give you a special ability to use in combat.
As you progress in the game, you will be swapping equipment and upgrading it, so your abilities will be changing. But this also allows you to customise your hero. If you like certain abilities - keep them. Others not working? Well, swap the equipment and get new ones. How you combine abilities in combat and play to your strengths is key to overcoming some of the tougher 'bosses' and legendary monsters.
What people will geek out about (I hope) is just the variety of 'builds' (i.e. different ways you can outfit your character) that you can create. And these will vary based on your path and career. For example, an assassin may favour passive damage (venom, bleed etc) and daggers, whereas an inquisitor may concentrate on higher armour and defensive abilities. It is up to the player - and there is room to experiment.
So... lots of strategy. Check out the how to play section (I'm sure you have already) for more on the abilities in the game and the combat system itself. The combat system is designed to be really simple to pick up - but with the abilities, will give you lots of imaginative ways that you can pummel and blast your foes into oblivion!