I don't think I've ever played a system where combat is interesting to me in and of itself. Combat between the PCs and an NPC that we've come to know and fear? The best. Combat that has clear narrative stakes and will meaningfully direct the course of the story? Also good!
But combat as a bread-and-butter component of a game, the expected culmination of a scene, against fungible enemies that exist solely for the purpose — never figured it out, as either a GM or a player. I can have the enemies be distinct and interesting, or act in unexpected ways, etc, but I can never find the flow of it.
BUT I AM TRYING. So here are a few combat system ideas transcribed from my notebook:
Cards
What if the players were each dealt a hand of playing cards, with suits corresponded to moves or skills? And numbers corresponding to … hmm. The equivalent of dice rolls? And you can make hands of the same suit or number in order to increase effect? The fun of this would be in finding a perfect little card game and turning it into the heart of a combat system, so that players would want to get into combat just for the sake of playing the cool game. Or maybe it's more like Slay the Spire, where you want to get into combat to put your limited deck to use.
Drawing
What if players were required to draw combat — not the moves, exactly, but the outcomes. Like combat sheets would have an outline of a figure and the players would mark on the sheet what injuries were given or sustained. This feels like it'd be ideal for a martial arts game, where combat was really up close and physical. And … over the top? Which isn't where I'm naturally inclined to go. But it'd keep combat from feeling floaty. Also it'd be rad to compile a stack of sheets for all the fights a party gets into over a campaign.
Worksheet
Basically steal Burning Wheel's approach, where combat is a somewhat laborious mini-game, with moves mapped on paper in advance. Regardless of the exact mechanics, the best part of this was that it turned BW into a game where combat was either colorful and fast (if it was low stakes, a single dice roll) or thoughtful and slow (for important fights, out come the worksheets).