This is my favorite class/level game. Not a retroclone, but a very successful attempt to preserve the old-school feel while operating with more modern and flexible mechanics. The pie-piece approach to multiclassing is brilliant, and Luck Points answer all my complaints about hit points in old school D&D. The key dX mechanism models the shift from calm and professional to frantic and occasionally heroic. Read it for mechanical inspiration, play it for fun!

This game system has a very playable solution for every weird situation that has come up at and around RPG tables over the last 40 years. Suddenly have to figure out how strong an elephant is vs an ogre? Use the Size rules to quickly get to the bottom of it. Wish there were more gameable mechanics around conflicts that aren't combat? Arguments and Stealth are here for you. Want it to be easier to make your own character classes, weapons, armor, spells, and almost anything else? Revival has all of that, too! With one simple dice mechanic, the dX, Kowolski has made a system that is easy to learn and fun to master. Do you stay Calm and automatically roll a 10, go On Edge and roll 3d6, or become fully reckless and roll 1d20? Since NPCs are always rolling 1d20, you may eventually find that you can't remain Calm for long. This is a great, modern, every-stat-matters reworking of first-generation roleplaying games that still plays and feels like the original games. I promise it won't let you down.

Convoluted rules that wreck the point of OSR. If you can assume a base d20 or 2d6 system, why pretend it's OSR? It's a whole new system and a pain to learn instead. Meanwhile, the tone of writing is condescending and a major turnoff. I'd rather stick with The Black Hack, or Sharp Swords & Sinister spells, or OSE, or any number of other OSR games instead.

Awesome system, feels like an old school game but throws out all the mechanics you're used to and replaces them with stuff that makes the game way more fun for players. Combat is interesting and active without becoming the forefront of the game or overrun with fiddly bits. Even basic actions like stealth become their own minigames that offer meaningful choices to players. It is challenging to wrap your head around the first time, and it requires a lot of the GM to fill in the gaps (e.g., there is a whole mechanic for mutations, and the author does not provide a table for said mutations, you just have to come up with it yourself). It is also not easy to convert older content to the system, as the chasiss it's based on is very different from DnD and adjacent systems. If you can get past that content and learning curve, it is an absolute blast to run. Even if you don't like it at the end, there are so many good ideas here you can take and implement in your retroclone of choice.