When comparing 13th Age vs GRIN, the Slant community recommends 13th Age for most people. In the question“What are the best tabletop RPGs?” 13th Age is ranked 27th while GRIN is ranked 36th. The most important reason people chose 13th Age is:
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.
Ranked in these QuestionsQuestion Ranking
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 Zero dice required
GRIN uses a a standard deck of playing cards instead of dice.
Pro Narrative focus
With no intrusive dice or math players can focus on the story, with every action being resolved by the simple draw of a card.
Pro Creates excellent tension
GRIN uses a a standard deck of playing cards to create a fast paced and deadly feel that evokes modern horror films. One of the best horror games made, its ideal for Halloween or horror movie nights.
Pro Its great for single session games
Like any horror film, characters will die. Grin lends itself to deadly games and rally shines with 4-6 players and narrative arcs lasting 3-4 hours.
Pro Easy to improvise
With the intrinsic arc of a classic horror narrative built into the core mechanic, Grin can be an intuitive framework for improvised play.
Pro Unique mechanic
In true horror movie style, death becomes increasingly likely as the game's story moves irrevocably forward.
Pro Easy to pick up
The game has just one page of rules. It can be explained in a minute -- even to people who have no rpg experience.
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 Can be seen as too simple for some
Because each encounter has just two possible outcomes - success or death - there's little wiggle room in terms of roleplaying.