I'm really excited to be running Robert Schwalb's Shadow of the Demon Lord soon and thought I'd share some thoughts I've had about it recently. This will be an overview of things I like about the system first, and some in depth thoughts about the classes, magic, and subsystems later.
First of all, its similar enough to D&D that it plays well to gamers familiar with that system (or even new gamers familiar with fantasy tropes). The main mechanic is d20 based. There are orcs, dwarves, and goblins as Ancestries. What sets it apart is a darker tone with lots of horror influence, more adult themes, and the impending doom of the world that lurks over every campaign.
Orcs are a barbarian tribe warped with dark magic to become warrior-slaves for the Empire, until they rose up and overthrew the Emperor. Forbidden magic has horrifying splatterpunk effects--exploding eyeballs, literally shitting yourself to death--and taints the soul of the spellcaster who uses it. The potential for apocalypse, the "shadow of the demon lord", can manifest as plagues, hordes of beastmen, or awakening elder gods. These are just examples, and while the game has a setting provided, the themes and ideas are easily adaptable to a variety of homebrew settings, which I will be doing.
The system is simple but flexible. Robert Schwalb has worked on a lot of different rpg games and one of his design goals was to create a system that could be learned easily and didn't require mastery to play (*side-eye at you, 3.5 D&D and Pathfinder*). The bare bones mechanic is: roll a d20, get a 10 or better to succeed. That's it. Your only numerical bonuses will be from your attributes--Strength, Agility, Intellect, and Will. These bonuses will vary from -2 to +5 for typical player characters. Situational or class bonuses are called Boons or Banes. For every Boon you roll a d6, taking the highest one and adding it to your roll. Banes work the opposite and the two cancel each other out one-for-one. The DM is free to adjust difficulty of an action by applying Boons or Banes to a roll, and the roll-all-take-the-highest rule means less math and prevents a task from ever being too easy or too difficult.
Next I'll dig into the class system, which I love.