When comparing Open d6 vs Heroes Against Darkness, the Slant community recommends Open d6 for most people. In the question“What are the best tabletop RPGs?” Open d6 is ranked 22nd while Heroes Against Darkness is ranked 33rd. 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 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
Pro Focuses on simplicity
The game uses a single "d20 + modifier ≥ target" mechanic for everything. Characters can be created in less than 5 minutes. The writing is concise and clear.
Pro Deep, without being cluttered
A lot of meta-tools such as templates, etc, that make combat encounters incredibly simple to construct. Great tools for creature-building. A lot of good information on world-building. You can make any type of game efficiently, from hack-and-slash to role-playing. If you have played in a D&D campaign, this is a great choice for your first outing as a GM.
Cons
Con Complicated magic system
Con Requries prior knowledge of RPGs to completely understand
Some knowledge will be required to understand the rules as there are some unexplained conventions that are presumed to be understood.