Now that I've begun running my LL game proper (as opposed to the one-shot trial run a few months ago), I've decided on my set of house rules to tweak the game to my tastes. It's open to revision depending on how things work out in-game, but it's mostly final if not playtested.
The rules are:
Strength, Dexterity, Constitution and Charisma work as described in the rulebook, except that Prime Requisites are removed, so these attributes don't modify experience earned for any class (ability score minimum values for demihumans still apply). Instead, Intelligence modifies experience for all classes, 5% per modifier point (i.e. -15% for Intelligence 3, -10% for 4-5, -5% for 6-8, no modifier for 9-12, +5% for 13-15, +10% for 16-17, +15% for 18). Wisdom modifies all saving throws, not just magic.
When creating a character, the player rolls 3d6 in order, nine times. The first six rolls make up the six attributes in the order: Strength, Dexterity, Constitution, Intelligence, Wisdom, Charisma. The final three are floating results that can be substituted in for any of the six attributes (or discarded if too low to be any use).
CLASS-BASED WEAPON DAMAGE
All classes can use all weapons (apart from physical size limits), but the damage done is based on the character's class, not the weapon. The damage die is equal to the classes' hit die type. The exceptions are for daggers or slings (which do one die size smaller) and two-handed weapons (which allow the player to roll damage twice and take the better result).
On a natural attack roll of 20, the result is a critical hit, scoring maximum weapon damage. Blunt weapons cannot score criticals.
When being raised from the dead, a character must make a save versus death. Failure means that something of the character doesn't quite make it back from the Fugue Plain, so his Charisma attribute drops by one point. If this would reduce Charisma below 3, the character doesn't come back at all and is permanently dead save for divine intervention.
Demihumans can increase hit points after reaching their level limit. Every 200,000 XP above the minimum XP for their last level grants one additional HP (or a reroll of HP - see "Hit Points" below). This should be noted on the character sheet by writing a + after the level - for instance, a Dwarf with maximum level plus 2 HP writes "12+2" in the level box. Saving throws and other features do not increase beyond the level limit.
Note that the standard race-classes only represent typical adventuring members of their races. If a player is dead set on an atypical demihuman character (like a dwarven thief), he can combine class and race features to create a special class (e.g. Dwarf Thief) - subject to DM vetting of course.
This will be handled informally unless this leeway is abused.
Characters get maximum hit points at level 1. At each level up, the character rolls his entire new hit dice, adding Constitution modifiers, and takes this roll if it is higher than the current hit point total, or keeping the existing hit point total if that's higher. Example: a level 1 Fighter with 14 Constitution gets 9 HP (max d8+1), and at level 2 he rolls 2d8+2 for HP, keeping 9 HP if the new roll is lower.
At each level beyond Name level, the player chooses to either take the fixed hit point addition, or to reroll all the hit dice and then add all the fixed hit points. If the latter option is taken, the character still can't lose hit points even on a low roll, but does miss out on getting the fixed hit point(s) that he would've had from the first option.
Magic-users (and other arcane classes like Elves) prepare spells rather than memorising them, and don't need to have their spellbook to hand to prepare spells that they know. The spellbook is only required for learning a new spell (scribing it into the book is a necessary part of the learning process) and for any magical research; the spellbook is a workbook and notebook rather than a reference work. Scribing a spell from another magic-user's spellbook takes days at least (if not weeks) of uninterrupted work, making trading spells a risky measure of trust since spellbooks are very time-consuming to replace.
Magic-Users and Elves start knowing Read Magic, one randomly rolled first level spell, and one chosen spell at both first and second level. The second level spell can't be used until level 3 of course; it's advance study in anticipation of increased magical skills.
Before making a melee attack roll, a player can choose to make a power attack, taking a 4-point penalty on the attack roll to gain 1d4 to the damage if the attack hits. Stronger power attacks are possible: -6 to hit for +1d6 damage, -8 to hit for +1d8 damage, -10 to hit for +1d10 damage, -12 to hit for +1d12 damage.
Players roll a "defence" against the attacks made against them instead of the DM rolling for the attack. The DM declares the number of attacks (splitting by type if applicable, e.g. claw/claw/bite) against a PC. The player rolls his defence against them: a d20 plus his AC, and declares the result. A lower result is better. If the result is equal to or higher than the attacker's THAC0 (including all modifiers into the THAC0 score) the attack hits, otherwise it misses. A natural 1 is an automatically successful defence, and a natural 20 is an automatic failure, suffering a critical hit (unless the attack is of a blunt type).
Note that this is a procedural change rather than a rule change: it's mathematically identical to the standard method of the DM rolling for the attacks.
The Thief class gets 1d6 for Hit Dice.
Clarification on the scope of Thief skills: Starting percentages may be low, but they represent the chance of exceptional feats. "Move Silently" is the chance of complete silence, which isn't always needed - moving quietly is usually enough to give a chance of surprising an enemy, and that doesn't require a roll. "Hide in Shadows" is the chance of remaining unseen in direct line of sight with only shadow for concealment - having real concealment can improve the chance or give automatic success. Players may be able to find traps (and find ways around them) by experimentation and cleverness, without having to succeed at "Find and Remove Traps" rolls.
TWO WEAPON FIGHTING
A character can wield a one-handed weapon in each hand. Attack and damage modifiers are based on the characters' Strength or Dexterity modifiers - whichever is lower - and on a successful hit, the player gets to roll damage for both weapons and choose which one hit (this option does not add multiple attacks).