When comparing 13th Age vs Risus, the Slant community recommends Risus for most people. In the question“What are the best tabletop RPGs?” Risus is ranked 12th while 13th Age is ranked 27th. The most important reason people chose Risus is:
Risus has a very minimalist rule system that breaks down all actions to their core function. Risus comes with a super short, four page rulebook (available in many forms and formats) that's easy to read, includes examples and has a bit of humor thrown in to make the process or learning more enjoyable.
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Pros
Pro The game is built for people who've done it before
The world is half built, letting you get in and leave your mark. Each class plays mechanically different than other d20 versions. Skills are placed by backgrounds. It's a short hand and interesting way of playing DnD.
Pro Long lists of skills are gone completely
And covered by backgrounds (much like FATE or Cortex+) so that players aren't searching through lists of skills and what they can do constantly.
Pro Gonzo without the grid
13th Age has some very gonzo fights with party combos, lots of variable powers for monsters and PC's but as a simple set of rules for combat that speed it up without losing a lot of options.
Pro Can be taught in less than 10 minutes
Risus has a very minimalist rule system that breaks down all actions to their core function. Risus comes with a super short, four page rulebook (available in many forms and formats) that's easy to read, includes examples and has a bit of humor thrown in to make the process or learning more enjoyable.
Pro Very flexible rules
Risus is not confined to a selection of pre-defined character-classes, settings or abilities. Characters are described via clichés such as Witch Doctor, Gambler, Musician with a number of dice assigned to each cliché that are then used in challenges that relate to the appropriate cliché.
Pro A large following that provides a lot of content
A large amount of adventures, artwork, characters, clichés as well as optional rules can be found for Risus. An excellent resource for all aforementioned things as well as many others is Risusiverse, a fan-made website of all things Risus.
Cons
Con Too similar to 4th
Con The Icons and the PC relationships to them can confuse
Can be confusing, especially for new players.
Con It doesn't really do anything new, it just looks pretty
Con Little guidance can be found for GMs and players
Some prior understanding of how an RPG is played and what is the role of the GM is required as the rules cover only the very core of the system.