A western style rpg akin to skyrim but with a combat system more similar to dark souls. Various weapon types (swords, claymores, polearms, daggers, whathaveyou) can be matched with different fighting stances so that even using the exact same weapon, characters would still attack, move and behave differently. If anyone is familiar with how the swing system in dark souls works, in how different weapons have different strong, weak, dodge and roll sort of attacks, think that as its own option separate from what weapon you use (though still restricted to certain weapon classes). Basically, you can find and decide on a combat style to determine move set, and then decide a weapon that fits it best, or best for the way you play. Even better if some styles can work for multiple weapon types, though not any one for all.
Next, do something similar to the magic system, where as casting can be done different ways for different benefits or at different costs. A standard cast like a lighting throw compared to an evocation that marks a spot on the ground a second before it bursts forth. A kamehamaha sort of charged spell that can be released at the right moment used at the expense of mobility when casting compared to a blood right hand-slash that costs some health for an added punch of damage.
Now add that back into enemies you encounter, so that every time you see a bandit with a sword, you have to actually take a moment to assess the style of fighting they use a little when fighting. Not only would this remove a little predictability during the million cannonfodder march to the final boss, but it could add so much depth and character to those otherwise unexciting foes. And if you add in even a bare bones personality option to each of them (maybe with behavior tied to randomly generated options in things from hostility to obedience/group loyalty to intelligence/courage). Then add a few levels of leadership to some groups, so that bosses have commanders and all have minions. That way, with the small addition of options, every bandit encounter could be different. In one, the boss might have a trope of loyal minions who eagerly rush at his command at the drop of a hat, in another, the leader may not want to fight and will just let you go unless you attack first, though his commander may not be loyal enough to obey that order and may attack you on their own. In the final, the leader may give up when injured a little but his own men turn on him in a coup before they try to finish you off. And all while feeling unique characters in their own right. Add in a random name generator so that they are not always seen as "bandit", and suddenly you have a deep and engaging game that keeps you on your toes, keeps the combat fresh and with just enough unpredictability and still has the large, open world enjoyment and exploration.