One of the big recurring problems in game design is that players are spoiled. They're used to being able to save anywhere and they want to know their exact statistics. They want to know that they have 509hp left and take approximately 7hp damage per hit, and the boss has 2030hp left and they do 34hp per hit, therefore they should survive the battle with approximately 90hp.
But I've finally come up with the solution - a *general* solution, in fact, not a specific one. Let the player do it if they want, with a penalty. Make it hard to switch on and off, or in the case of a single-player game, impossible. And usually it's not hard to figure out the penalty.
The penalty for the "save anywhere" thing is a bit more obscure, actually - for that one, you just link it to the difficulty level. Want to play it above "Pansy" level? Well, you're going to have to have some skill then, and I'm not referring to hitting the quicksave/quickload button a lot.
The penalty for the HP meter, though, is brilliant. (I say so modesty.) It's easy. If you want to know *exactly* how many HP you have, you just won't have as many. That's all.
Of course, we still need *some* indication - I think one of the better ways would be a visual indication of how much damage you have. A health meter (perhaps a blocky one, so you can only see in increments of 10%) would work also. Smooth is okay, but still gives you a lot of indication.
One of the other big problems associated with not letting the player see numbers is not letting them compare things. "But is a Heavy Steel Breastplate better or worse than a Rusty Grandmaster's Bone Cuirass? I DON'T KNOW!" Well, sure you do. It's easy. Just provide a "compare" function, and the computer says "Heavy Steel Breastplate is much better at blocking slashing attacks, but is slightly inferior with lightning resistance."
And if you want the pure numbers, go buy an identify spell.
It'll cost you, though.