The game is billed as "Old-school sword & sorcery heroics for a single player and GM".
What's my experience with it?
I've been working on the playtest, so as a long term campaign, I don't have the experience of how it will play out in that way. But for one-on-one one shots, I've done some playtesting, up to an including the release candidate version.
Why do I recommend it?
Though it closely resembles the standard D&D type system, there are only four main mechanics over 8 pages in the rulebook. Rolls are only called for if the DM calls for them as they would reasonably tax the hero- otherwise narrative takes the day. As the characters are supposed to be that hero, failure should be because of mischance at some great trouble rather than a lack of skill on their part. For me, the familiarity made it easy to run and explain without constant reference. My counterpart was also familiar, so it made it that much easier, but I don't think it's particularly hard to pick up.
Though it does reference movement and such, we played it with only references to distance and such, and no use of a battlemap nor any similar crutch.
Quick character creation
Standard character creation isn't that involved- roll attributes, choose race and class, the choose a number of traits. Traits are a few words to describe something a character has been or is good at doing. In anything that crosses that particular trait, a character is considered skilled/proficient, and that drives the use of narrative rather than skill checks in those situations. For example, if someone has the trait "Wanted to follow his father as a fisherman", then you'd assume he knew how to sail if it came up, so there would be no skill checks unless there was an unusual storm or some threat was chasing him.
In addition to this, there are tables for quick character creation with example traits- roll a few dice, and you have your character.
Doesn't require a party of more than one
This game is made for one on one play. In fact, you have to adjust for the presence of more than one PC if you intend to tailor it for more than one. Why is that?
- All damage dice are scaled down for heroes, and up for monsters. For heroes, each die that rolls 1 does no damage, 2-5 does 1 point, 6-9 does 2 points, and 10+ does 4 points. For NPCs, they can take as much damage as their hit dice.
- The PC has a fray die, that represents incidental damage to lower level opponents Each round the hero is in combat with opponents that have the same or less HD than his level, the die can be rolled, and the damage applied to any opponent that qualifies.
- In the case that the hero is left with a situation that their skills cannot handle, they can 'Defy Death' Personally, I think that the skill should be called Defy Danger as in Dungeon World, because it works similarly to that. It's a last ditch effort to overcome some situation that they are actually not fit to perform, whether it's get past a magical ward, break into a trapped chest, or resist some sort of unresistable damage.
There's also a whole area on converting things from other adventures for one on one play, and tips on changing GM mentality for solo play. In fact, the conversion was the reason for the way that damage was scaled rather than just changing to a different way of inflicting/taking it.
Easy to GM on-the-fly.
Scarlet Heroes was made to be a sandbox type of game, and to exploit the shift to solo play with more personal stories, rather than pre-planned arcs. There's a whole section on this shift in paradigm, and how to generate things on the fly to make the game tailored to the player's experience, rather than the GM's preconceived idea of a campaign. The GM basically sets up the situation, and allows the PC to experience it however he chooses. As GM, you can put as much or as little preparation as you desire into making a story arc, but are encouraged to not assume that the PC will even encounter that particular preparation.
The built in setting is a summary of the Red Tide campaign setting from a previous product. If you want to use the whole setting, that source is very much recommended, but by no means necessary. It's a really cool setting with more than a bit of a Chinese and Japanese flair (not combined, just adjacent)- very old school in its feel.