The 6 characteristics generated by 4d6 drop lowest and assignment is pretty common within D&D style games, but is slightly uncommon in OSR games which often use the less high powered 3d6 in order. This does help match the idea that the characters in Scarlet Heroes are extraordinary individuals.
Only 4 classes are available by default: Cleric, Fighter, Magic-User, Thief which is not that uncommon in OSR games, however it is possible to add classes if required or hack them to match the setting. An unusual feature is that classes are not limited to particular weapons, but the damage done is limited by the class. Races are limited in the classes they can choose but there are not the racial classes familiar to players of B/X D&D, so it is more like OD&D in this aspect.
Character traits are a feature that help flesh out a character by giving areas of expertise to them. This is at a fairly loose grained level so the trait might be 'Former cultist' or 'Knows many thieves' rather than something like 3e D&D skills and feats with strict definitions. They are used to give bonuses on checks which I will explain in the section on mechanics. There are trait bonuses for races and classes and no trait can have more than 3 points in it.
Weapons are very simplified to help speed play, so they are divided into types rather than having the traditional splits into Short Sword, Long Sword, Battle Axe, Rapier there are one-handed weapon, two-handed weapon, bow or crosswbow, etc. Armour is more limited by type than some OSR games and plate is properly expensive. This can avoid the endless shopping lists in some games and the golf bag of weapons that was encouraged by some damage reduction rules like the ones in 3e D&D.
The equipment list properly reflects the background with a 10ft bamboo pole, rice wine and beer as changes to the default descriptions. The list is not one of the massive ones found in some OSR games but certainly contains enough information to run a game from and to work out other costs.
A quick generation section exists for characters allowing rolls against background for each class, innate qualities and relationships which can be used with the traits. Useful also if a GM wants to create a protaganist style NPC or to get a feel for the setting.
This is where things really vary from most OSR games in checks, saving throws and combat.
Checks and Saving throws both use 2d8 with modifiers applied with a target number based on the difficulty of the check or the level of a spellcaster that is throwing a spell for a save vs magic. This has a rule that a roll of 2 is automatically a fail and a 16 is automatically a pass regardless of the target and modifiers. Saving throws are usually against the most relevant attribute, so Constitution for poison, Wisdom for magic. It does note that checks in particularly should only be used where necessary, particularly where a character's traits would imply a solid set of skills in an area.
Combat uses to hit and damage rolls but these again work differently to normal OSR games. To hit uses a formula of add the hero's attack bonus, attribute modifier and the target's AC to the roll of a 20 sided die and a total of 20+ is a hit. Automatic success and failure are on natural rolls of a 20 or 1. Damage is rolled in an unusual way with the amount of damage being from a cross reference of the roll of the relevant damage dice to a table - a roll of 1 is no damage, 2 to 5 is one point of damage, 6 to 9 two points of damage and every roll of 10+ is 4 points of damage. Against opponents this damage is applied to their hit dice. The reason that the hit dice for monsters have been retained here is for easy compatibility with other OSR games when in reality they are hit points.
An additional factor in the combat is the Fray dice. This is an additional set of damage done by the hero and is one die of their class damage type, e.g. 1d4 for Magic Users, 1d8 for Fighters. The damage done by this is on the same basis as the damage rolls for hits in combat and for all classes except Magic Users applies only to opponents with the same or less hit dice than the hero has levels. A MU has the ability to apply the Fray damage to any single opponent of any level which does make them more lethal.
All damage flows with any additional damage left after killing the first opponent being put onto the next opponent meaning that low level opponents can be cleaved through rapidly.
Spell casting can be interrupted by a successful hit but as a hero goes first in the round a Magic User hero will normally be successful. The save difficulty is calculated as 9 plus the level of the caster or hit dice plus any relevant traits the hero possesses.
Defying death, this is an optional rule that allows a hero to overcome what would normally be a fatal situation or deal with a challenge that would normally be beyond them. The hero makes a check against their level with a number of D4 damage dice which is then compared to their hp. If the total damage is higher than their hp they fail and are reduced to 1 hp, otherwise they succeed and I presume their hp total is reduced by the damage. That is the only part that is not completely clear in the beta pdf description.
Turning undead can be done by a hero with any levels of cleric by rolling one d8 Fray die per Cleric level they have applying this to any undead within 30 feet. The undead they can affect are based on their total character levels so a hero with 3 levels of Cleric and 2 levels of Fighter could attempt to turn a 5 hd undead. It would be fairly uncommon for this to work though and this helps keep high level undead like the types of vampire as properly scary opponents.
Injuries and Healing
Even a hero will die if their hp drop to 0, though it is noted that a GM may wish to avoid this in their campaign. Healing is gained by overnight rest with a hero regaining 1 hp per level, and twice this if they rest for a full day with medical skills being applied to their wounds. A monster or NPC would heal 1 hd per day. It is noted that a GM may wish to allow a hero to heal through carousing for a day if that is more suitable to their character, this reflects a S&S feel where Conan or Fafhrd would still drink and wench despite their injuries.
Experience is usually awarded per session with the amount of experience required to level up increasing each level, e.g. 5 experience for 3rd level, 9 experience for 4th. A character will receive a fixed amount of extra hit points, additional Attack Bonus and trait point and class based abilities will also increase such as spells. Heroes can multiclass quite easily but the impacts of this on them are quite dependent on the classes involved.
Movement and encumbrance are deliberately kept simple as this is not a strict resource management game like some OSR games and the GM is left with a fair amount of discretion around how the hero's equipment will burden him and at what point the encumbrance will affect their abilities. Travel includes shipboard rates as the default setting has a lot of islands meaning that it will not be unusual for a voyage to be part of a journey.
So as a partial review I thought I'd comment on what I've read and what I think. For an OSR game it is unusual in concentrating on a more heroic style of play rather than the stereotypical resource management and niche character roles. It looks like it would work well for a classic Sword & Sorcery game that was inspired by R.E. Howard and Fritz Leiber's writings though the setting is more oriental.
In a way the thing that the rules remind me of conceptually rather than mechanically is many of Two Hour Wargames' sets of rules which allow for a star character to have heroic characteristics including being able to cheat death.