Great thread.
I like simplicity when pared with more complex presentation. Quake is frankly extremely simple, but is combined with deceptively complex encounter and level design and impeccable atmosphere, keeping you engaged moment to moment without overloading you. You can hit a flow state in Quake that lets you smash through levels while enjoying every minute of it.
I dislike simplicity when its used to divorce player agency from control. Games like The Last Of Us are dead simple so you can't fuck up the animated movie the developers wanted to make. Doesn't take long before my brain turns off and I simply lose interest, regardless of how expensive the cutscenes are.
I like complexity that enables expression. Dark Souls is both simple and complex, where you really only need a small number of buttons for the entire game, however the mechanics attached to your actions are very deep, allowing a huge amount of build variety and thus gameplay style choices.
I dislike complexity for complexity sake. Doom Eternal, a game that on paper I should adore, simply has too many mechanics that don't add anything in terms of play style choices, but punish you for not using them. Tracking four separate cool downs while hot swapping weapons isn't depth, it's busy work.
The perfect mix to me are games like Remnant II and Resident Evil 2 Remake, where it controls well, has solid encounter design, lots of secrets and depth, but whittles away anything that doesn't invoke player choice or agency. It sits right on that sweet spot that keeps me coming back again, and again.