Section 5 is a space opera espionage game that sits at sort of a tonal midpoint between Eclipse Phase and Babylon Five. It is based on FIST, but the FIST rules are not required to play this game.
The PDF is large, with a nice bold cover, cleanly organized text, and an easy to use character sheet. The bulk of the layout is just bare print, but it's all perfectly readable.
Setting-wise, this is a big hard fi solar system with a lot of geopolitical intrigue, and so learning the game means spending a little bit of time learning the setting. The tldr is that you play as agents of a nominally progressive fuel consortium trying to prevent species-ending weapons development by destabilizing other factions.
The overall angle is a bit Delta Green and a bit Eclipse Phase. You're not the A Team. You're disposable assets doing dangerous work, and the setting treats you like it.
There's an expanded setting wiki at worldanvil that the book links to, and it's not strictly required for play, but the GM may want to skim it anyway. It's hard to run geopolitics without having a good grasp of all the pieces in play.
Mechanically, Section 5 works very similarly to core FIST. There are a few new mechanics like tickdown (rolling a d6 to set a timer), and roll bonuses have been broken into a wider Skill list. There's also a nice addition to the game's lethality, where if your character dies on a mission, you immediately reroll a new PC and are inserted back into the mission with the goal of joining up with the rest of the team.
For character creation, the process is much the same as standard FIST, although TRAITS are sorted into categories by profession (civilian, military, criminal, etc) and give lots of small bonuses to Skills. These new TRAITS are mostly custom built, and a lot give you cool choices rather than just straight bonuses.
Section 5 is written very thoroughly, just like core FIST Ultra, and there's plenty of support for GMs threaded throughout the book. Guidance is also given to players, and the dice system and character building mechanics are easy to learn and player-friendly.
Overall, this is a neat, thorough, and genuinely very high effort FIST mod. If you like hard fi, espionage, and simple, graceful rulesets, give Section 5 a look!