1) I've never played Harn.
2) I've played a bunch of D&D. I play every Monday. It's a cool game. I like it a bunch.
That said, is it possible that gaming elements in D&D are more childish than in Harn? Can a gaming element even be childish?
Hit Points, for example. Definitely more abstract, and there's the old problem of a 6th level fighter who laughs in the face of ten guards with crossbows, because even if they're all pointed right at him, he knows that they need an 18 or higher to hit, and he can take the damage easily. Or a 10th level fighter who considers jumping off a 100' cliff a viable and efficient way to get to the enemy wizard at the bottom (average of 35 points damage, and even if it's higher than 50, his Fort save is high enough to make Massive Damage Death unlikely).
Proponents say, "You're missing the point. The cool thing about D&D is being ABLE to play someone who can dodge eight crossbow bolts, like Trinity in the Matrix (who one could say was hit for trifling amounts of damage by bullets that grazed or barely missed her)."
But there's the issue of the Power-Fantasy Wish-Fulfillment factor. I'd argue that the more powerful your characters can easily become, the more prone your game is to power fantasy play -- that awkward and cringeworthy event wherein gangly unpopular teenagers become melee gods or fireball-flingers and general munchkinism ensues. From what all the Harnites have said, their system makes it harder to go all power-fantasy happy -- since a powerful guy can be maimed or scarred or lose a couple of fingers real easily, even on a good day.
I open myself to flames with the following:
Argument 1: D&D is more abstract, and therefore less realistic, than other games, like Harn
Argument 2: D&D enables greater power scaling (as in, a character gets a lot more power, to the point where they can shrug off things that would have killed them early-on) than other games, like Harn
Argument 3: Games with greater power scaling are more prone to idiot munchkins who like to talk about what level their character is, how many things he has killed, and how many weapons he has -- which gives a bad name to the system they use, regardless of other people who use it responsibly...
Argument 4: Games that are less realistic benefit from generally being easier to manage, but have the potential for enabling a less mature gaming style
1: Don't know Harn -- tell me.
2: Don't know Harn, but this seems to be what they complain about.
3: This makes sense to me, but maybe there are Harn munchkins too. It does seem, though, like games where you get powerful create power fantasy games -- which are arguably less mature. Although Paranoia didn't promote hugely mature play, and you were always two steps from death there, anyway...
4: In some games, they describe the blow glancing off the bone and cutting along the leg with a jarring shock of pain. In D&D, we can have people blown across the room by a fireball who then fall off the wall, leaving a little them-shaped spot in the charred pattern, and continue fighting. Not everyone does it that way -- some people elaborately describe blows that just miss, or that graze you, or fireballs that you take on the shield and therefore only lose an eyebrow from -- but the potential for silly play is there.
At the moment, my conclusion is that while a given D&D game can be mature or immature, the game itself enables immature play in ways that other systems do not. However, my OTHER conclusion at the moment is that "childish" is an inherently loaded term. Anything you play on your GameCube is childish. Roleplaying itself is a GAME, and as a game, it is inherently childish. But when you say it as a loaded term, it gets ugly.
In my game, sometimes I describe the combat in detail, and sometimes I just wanna do hit point damage because I want to get to the next fight. Sometimes people duck past the fireball to take only a bit of damage relative to their maximum hit points, while other times they take it full in the face and say, "Ah-ha, thank goodness I wore my fireball-repellant today!" after taking weenie damage. It's a game I play with my friends. We have fun. Calling us childish is the pot calling the kettle black.
-Tacky
Edit: Me types good.