Lumen is a fantastic system, and the SRD is a refreshing take on how to present the rules of the system.

Second thing's first: the presentation. This SRD isn't just a dry, procedural look at the game mechanics bereft of examples or personality; totally the opposite! This SRD features the rules, gives you tons of examples and optional variants, and does it all with a breezy conversational style. The language tells you "here's a thing that's cool" and then sells you on all the cool things it can do, and that makes it fun, engaging, and eye-opening with regard to the myriad possibilities the system presents.

Back to the system: it expertly melds the bones of Powered by the Apocalypse games to the spirit of Forged in the Dark (which admittedly already have lots of shared DNA), but it does so with an extra dose of "mechanics over narrative." That's not to say it's not a lite, highly narrative game: it most certainly is. But it is to say that the GM -- even though they don't roll any dice -- still has a certain degree of mechanical interaction (how opposition works) and resource management (how "drops" work) that I personally sometimes find lacking or too nebulous in many PbtA or FitD games. It's still definitely rules lite -- about the same level as Fate Accelerated, maybe slightly edging towards Fate Core -- but there's enough mechanical grit in there that you can find a lot of potential for mechanics-based tactics and strategy. Which makes sense: this game is meant to feel like shooter-looter style video games, and it does this perfectly. There's an underlying "system" that's tightly focused, but leads to a ton of fun, fast-paced, high-octane action.