Before anyone asks - no, I haven't had time to read the rules for Mages & Monsters. Apparently running 12 (plus) Days of OSR Christmas with all of it's moving parts is damn time consuming ;) I've actually known about the game for nearly a week and was hoping to find time to read it and it hasn't happened. So, I'm throwing it out to you all to investigate at your leisure.
It does look interesting, but I'm not sure how much of a need there is for yet another ruleset that houserules what has come before it.
From the FAQ
Q: How is M&M different from other OSR RPGs?
A: M&M uses the classic OSR design basis of other retro-clones, but combines them with modern d20 mechanics. Compared to the classic basic, expert, or advanced fantasy RPG, you have more consistent mechanics (example: ascending Armor Class and higher-is-always-better rolling), simplified combat process and saving throws, fewer restrictions on races and classes, and greater choice and customization in class abilities. Compared to other d20-based games, you have a more streamlined game that doesn't overload players with choices and offers easier rules adjudication, simpler stat blocks, and easier adventure design for the Game Master. Plus, it's free!
- The initial pdf release has four races (Human, Dwarf, Elf, Halfling) and five classes (Cleric, Fighter, Mage, Thief, and Swordmage -- the latter is a fighter/mage hybrid). Any race can take any class; all classes are 20-level progressions with class abilities "built in". You can fully replicate the classic basic/expert class system with this document.
- Classes allow choices of skills (a simplified attribute-based system -- proficiency or no), weapon proficiencies (with an option to increase in proficiency), and some classes have a fighting style proficiency that allows other fighting options. However, there is no feat system as in d20; choices are internal to the class.
- There are no restrictions on skill choice, or weapon choice, so that players can more readily tailor to a concept (these things are balanced in otehr ways to keep classes distinct).
- Classes have a base attack bonus and three-save progression (Fortitude, Reflex, Will) and the d20 mechanics of "roll high against a DC" is used, with a fixed DC progression (Easy, Average, Difficult, Very Difficult, Nigh Impossible)
- Classes use a unified progression; no balancing classes against each other by using XP advancement.
- Math is flatter than the base d20 system (max BAB for a 20th level fighter is +6). Attack rolls and AC stay very flat with relatively small increases over time; damage and hit points scale more.
- There is no multi-classing; it is "built in" to hybrid class designs like the Swordmage which allow an equal progression in fighting and spellcasting (but are not quite as capable in either as a single class). The plan is to increase the number of hybrid classes significantly in the Expanded rules.
- Spell lists are more limited but spell descriptions are more flexible and spells allow power scaling to compensate for fewer choices. Spell power does not depend on caster level in the majority of cases ... yet a more powerful mage can still throw a more damaging fireball than a low level mage.
- Monster stats are "one line" stat blocks like the old basic game.