It's difficult, and in my opinion, pointless.
It's immersive at first, not having to see the magic compass or the obstructive cursor and magically knowing where any combatants are even in a dark cave. But it kinda kills immersion when you have no idea how your character is feeling. I feel like the MP/HP/SP bars are necessary for this since there aren't any decent indicators of how tired or hurt they are unless they're at their limit (gasping for breath for low stamina and the screen turning blurry and red for health).
You can't actually "feel" their pain or exhaustion and any injury is met with the same grunts and yells no matter how much damage is done. Using Garrett from the Thief series as an example, when he's hit by a trap or sword, he'd give the same reaction as a PC in the Elder Scrolls. When he's hit by a particularly powerful attack, like a fireball or a mallet to the face, he'd scream. Like, SCREAM. The damage was proportional to the loudness or his yells most of the time and I didn't have to look at the HP meter to know how much more he could take. How do characters in Skyrim react to a Fireball spell that takes 75% of their HP? "Ouch!"
Well, it wasn't perfect, but it's the right idea. If fatigue and injuries showed in the way your PC attacked or moved, then it wouldn't be so bad. Magic too, although I admit that I usually don't worry about how much magica I have left when casting. It can be just as dangerous, though.