When comparing Monsters & Magic vs Open d6, the Slant community recommends Open d6 for most people. In the question“What are the best tabletop RPGs?” Open d6 is ranked 22nd while Monsters & Magic is ranked 42nd. The most important reason people chose Open d6 is:
Open d6 includes rulebooks for Fantasy, Adventure and Space settings.
Ranked in these QuestionsQuestion Ranking
Pros
Pro The Effect Engine
The game uses a single core mechanic, which is flexible enough to cover a wide variety of situations. This helps GMs immensely when characters want to do things that aren't already covered in the system.
The mechanic itself works thusly: all rolls are 3d6 + modifiers minus difficulty. The result is how many effect points the player can apply to the action -- or, if negative, how many consequence points their opponent can apply to a reaction. Dealing damage is one use of effect points, but there's a limit on how much can be dealt at once, so additional effects (e.g. distracting, disarming, unmounting, etc.) see constant play instead of only being used rarely or by super-specialists. This also means failure is interesting, since it results in consequences!
This mechanic is used to do everything, and the game essentially consists of nothing but examples of how to use it.
Pro Interesting combat
Attacks generate effect points, which you spend to do things to your opponent. However, the amount of damage you can do is limited, which forces players to do other things... and the effect system is broad enough that these can be things like cutting off a carrion crawler's tentacles, knocking an opponent's sword out of their hand, and so on. Failures on attack generate consequence points as well, which your opponent can use to do things to you.
Pro Mental defense and hit points
Characters have a "Mental Defense" score and "Mental Hit Points". These are used to help provide a unified system for handling social encounters and mental attacks via magic.
Pro Includes rulebooks covering the more common genres
Open d6 includes rulebooks for Fantasy, Adventure and Space settings.
Pro No special dice required
The game can be played with common six-sided dice.
Pro A simplified variant, called Mini Six, is available
Mini Six is a fan-made variant of Open d6 that aims to be a distilled version of the Open d6 system.
Pro There are theme-related books available to start various types of games
D6 Space is West End Games old "Star Wars D6" game with all of the licensed Star Wars names removed. It's a stand alone complete game.
D6 Fantasy is a standalone ruleset for running a D&D type game with the D6 system.
D6 Adventure is a standalone ruleset for using the D6 system in a Wild West, spies, or modern adventure game.
All three have supplement books (Spaceship design, magic, aliens, etc).
Pro Each rulebook has a good introductory section
Cons
Con Not currently available in print
Is only available in PDF.
Con Few monsters & spells provided
The included rules have only about 20 monsters and 1st and 2nd-level spells. Third party publishers have supplements that provide more, or you can use ones from old D&D.