Here’s a video of Operation Black Swan which effected the capture of “El Chapo” Guzman. It’s helmet cam footage and should give you a good idea of how to describe combat sequences in your game.

It’s chaotic even if you had a good plan. It’s loud and disorienting, even when you know what to expect. (It would be no different with swords and magic — fighting is loud and confusing.) If you want to get the feel of the thing, concentrate less on the number of 10′ squares in the room; no one is pausing to say “gee, this looks to be a 50×20′ room, I now know my fireball will do…”

You might even misdraw the map for the initial portion of the fight, then reapportion the dimensions as people move through and realize it’s bigger/small than they thought; drop things on them that “should have been visible” (really, what could you see in portions of that video that were well lit?) They blow a perception (or whatever you’re calling it) test and that guy/goblin/alien/whatever that was hiding pretty much in plain sight gets the better of you. Damn that wizard for flashing his damn light spell right in your eyes! Or crap, my large friend with the two handed-sword didn’t realize I was inside the arc of his swing when he cut that monster in half; or Johnny over on Team C was a bit out of position and you thought he was the bad guy…good thing he had kevlar on.

Make it murky, stressful, and confusing.