This is not a review. It's gushing in autistic detail over a brilliant minimalist solution to an age old problem.
That being, generally, Hit Points. In the beginning you have too few, at the end you have too many. Hit Points are also the reason Demihuman level limits mostly don't work. There's a clever solution for all of this on pages 6-7 of Iron Falcon '75. I think it revitalizes OD&D and is a much better, cleaner solution than previous efforts. But it's hard to articulate without showing off.
In the system you don't get extra HP for high Constitution. Because your Constitution itself dictates your starting HP. From there on you gain 1HP/level if Fighter, 1 HP/2 levels if Cleric or Thief, and 1HP/4 levels if Magic User.
So let's do some math. 2.5 Mil XP for a 20th level fighter. That's a fighter with 3-18 + 20 HP. So the majority of even the capstone XP class will be inherent HP from their origin, for at least half their leveling career if not more. This fixes A LOT. But let's not belabor the math. Oh, to be clear, I will operate as HP usually operates here, we keep seperate totals for each multclass and the best result is what the character gets. If there's a Fighter class in the mix, it'll almost always be the Fighter class.
2.5 Mil XP (what's required to make a 20th level Fighter, the benchmark):
18th level Human Cleric: 12-27 HP Avg: 19.5
20th level Human Fighter: 23-38 HP Avg: 30.5
18th level Human Magic-User: 7-22 HP Avg: 14.5
20th level Any Race Thief: 13-28 HP: Avg: 20.5
Now this actually synergizes with another mechanic - Doubles and Triples. Rolling 10+ to hit grants full double damage. Rolling 20+ to hit grants triple damage. Fighters are the only ones who can logically get there, so it's an added boost to them. Back to math though, let's interface this with Race-Class level limits:
2.5 Mil XP: Dead Ends:
4th level Halfling Fighter: 7-22 HP, Avg: 14.5 DEAD END
7th level Dwarf Cleric: 6-21 HP Avg: 13.5 DEAD END
6th level Dwarf Fighter (<17 STR): 9-24 HP Avg 16.5 DEAD END
8th level Dwarf Fighter (18 STR): 11-26 HP Avg 18.5 DEAD END
6th level Elf Cleric: 6-21 HP Avg: 13.5 DEAD END
4th level Elf Fighter (<17 STR): 7-22 HP Avg: 14.5 DEAD END
5th level Elf Fighter (17+ STR): 8-23 HP Avg: 15.5 DEAD END
8th level Elf Magic-User (<18 INT): 5-20 HP Avg: 12.5 DEAD END
9th level Elf Magic-User (18 INT): 5-20 HP Avg: 12.5 DEAD END
4th/8th level Elf Fighter/Magic User (<17 STR, <18 INT): 7-22 HP, Avg: 14.5 DEAD END
4th/9th level Elf Fighter/Magic User (<17 STR, 18 INT): 7-22 HP, Avg: 14.5 DEAD END
5th/8th level Elf Fighter/Magic User (17+ STR, <18 INT): 8-23 HP Avg: 15.5 DEAD END
5th/9th level Elf Fighter/Magic User (17+ STR, 18 INT): 8-23 HP Avg: 15.5 DEAD END
Non-Dead Ends: 1/2 and 1/3 speed XP to advance
6th/14th level Dwarf Fighter/Thief (<17 STR): 10-25 HP Avg 17.5
8th/14th level Dwarf Fighter/Thief (18 STR): 11-26 HP Avg 18.5
4th/14th level Elf Fighter/Thief (<17 STR) 10-25 HP Avg 17.5
5th/14th level Elf Fighter/Thief (17+ STR) 10-25 HP Avg 17.5
8th/14th level Elf Magic User/Thief (<18 INT): 10-25 HP Avg 17.5
9th/14th level Elf Magic User/Thief (18 INT): 10-25 HP Avg 17.5
4th/8th/12th level Elf Fighter/Magic User/Thief (<17 STR, <18 INT): 9-24 HP Avg 16.5
4th/9th/12th level Elf Fighter/Magic User/Thief (<17 STR, 18 INT): 9-24 HP Avg 16.5
5th/8th/12th level Elf Fighter/Magic User/Thief (17+ STR, <18 INT): 9-24 HP Avg 16.5
5th/9th/12th level Elf Fighter/Magic User/Thief (17+ STR, 18 INT): 9-24 HP Avg 16.5
Adding the half-elf would be absurdly complicated and I already went through most of that for the Elf, Let's give the best case scenario for dead end and non-dead end:
8th/8th/6th level Fighter/Magic-User/Cleric: 11-26 HP Avg 18.5 DEAD END
8th/6th/12th level Fighter/Cleric/Thief: 11-26 HP Avg 18.5
Ok so lots and lots of basic math later we can see that surprise surprise the worst deal on HP isn't the Halfling Fighter but the Dwarf and/or Elf Cleric. Well it's the Elf cleric because he doesn't get 4th level spells AND his HP is the worst of the entire grouping (Constitution roll permitting). The Single Class Fighter has the best at average 30.5 HP at this benchmark. The fact that Thieves run a little faster than everyone else up the level chart makes them better than the cleric outside of the absence of Armor.
Thieves get two more boons on these 2 pages. The Thief Abilities Option makes their first level more survivable with a low ability of Hide in Shadows at 25%. Their starting Picking Pockets is boosted to 40%, which means a starting Thief may actually be fun to play. Perish the thought!
Lastly we have the Unarmored Combat option, which basically says your BAB is also a Defense bonus if you're unarmored. I'm not sure how well that works out.
So I said ALL that to say this is a masterclass in minimalist design for maximum impact. The only real downside I see is all those dead end class decisions. The simplest solution being that they aren't maximums, but instead we double all XP costs for levels higher than those. This works but is hard to visualize, as with multi-classing you're dumping XP in multiple experience buckets so making unattainable levels cost twice as much you're multiplying multiples, meaning the XP is 1/6 value for those who have exceeded their level limit and are multiclassed thrice. The math is somewhat hidden because of the experience buckets vs doubling numbers after a time. Prime requisites become more and less important, as they make a few early levels easier to obtain but it all evens out when the later levels cost the exact same regardless of ability scores.
