Briefly, I proposed the following;

Cut back certain bonuses, in particular the luck and weapon enchantment
ones.

Another part of the problem is that monster ACs do not increase with
player power. In general give monsters an AC bonus equal to their hit
dice, fudging some early and middle game monster ACs so they don't become
tougher in the parts of the game where hitting is actually hard.

Give monsters with negative AC player-style damage reduction, _but_ with
the player's surplus to-hit negating damage reduction.

That way, you'll tend to miss sometimes much later into the game, and even
when you no longer miss, more to-hit is always valuable.

This couples in with the twoweapon proposal; roll to-hit for both weapons,
attack only with the one that scores best; attack with both if the primary
weapon rolls a 20 [1] at Basic #2w skill, 18+ at Skilled, 17+ at Expert.
This makes twoweaponing useful for hitting more, not for doing cruel
brutal damage. Exercise the weapon skills as well as twoweaponing -
because the skill is now most valuable early on. Once you have a godlike
artifact, you don't want to two-weapon because tickling people with your
crysknife is distracting you from belting them with Grayswandir.
Conversely, a Samurai should use the two swords right out the gate. This 
is good because they are movie samurai not real ones. Enormously reduce
the to-hit and damage penalties that apply now per-weapon; at Skilled
two-weapon, each single attack should be just as good as a one-handed
attack.

All artifact weapons get a flat +1d4 damage when they don't get any other
bonus. Bingo, no more junk artifacts.

Shields; add a "shield" skill practiced by being hit with a shield worn.
At unskilled shield, all shields are AC 1; at skilled, the value is
doubled; at expert, tripled. Add a 3 AC "tower shield" with no special
properties.

Two-handed weapons increase skill and strength bonuses to damage by 50% at
Basic skill and 100% at Skilled or Expert.

Cap player hitpoints at some rough multiple of experience level.

Late-game monsters that just hit should hit hard, like minotaurs.
Recognise the way that player damage reduction makes one big attack better
than several small ones.

This gives a situation where two-weaponing is great for hitting, and is a
great boon to someone who can't get a decent artifact but can double what
they do get with a crysknife or similar - and unlike the current
situation, the incentive to use it is much higher if you can get a decent
skill. For an Expert, the damage output is still quite respectable.

Shields create a very powerful defensive option for people with the skill,
at the cost of spellcasting ease - and any special shield ability if a
tower shield is in use. This becomes more valuable with capped hitpoints
and hard-hitting monsters.

Two-handed weapons do cruel brutal damage - not as much as #twoweapon does
now, but still pretty hefty. This is not unbalanced given the lack of a
shield's defense boost and the cursed two-hander problem, and it restores
the Tsurugi to its rightful place as the best weapon in the game (c'mon,
it's a two-hander that Rodney can steal and cut you in half with).

This proposal tends to mean that your available skills will inform whether
you use twoweapon, a shield, or a twohander - at the moment from a pure
efficiency POV anyone who can twoweapon should.

I am open to suggestions for a bonus for characters (presumably
spellcasters) who fight with one open hand.

[1] IIRC NetHack TH rolls might be backwards, but never mind.

I missed that out of my grand unified proposal; cap the weight of the
offhand weapon based on skill (so an expert Samurai can just manage two
katana) and the onhand weapon full stop (so you can't twoweapon with a
lance or polearm).

And throw away 9/10 of the polearms. Sheesh.