Disclaimer: I received a free copy of this product for the purpose of this review.
This is a 52-page, full-color product - and as the cover notes, it's one of the first Starfinder-compatible releases! Let's get right into the meat of this, shall we? Pirates of the Starstream is broken into five major sections.
The first section is largely historical, with some history on pirates and a sample pirate code that characters may wish to follow. This is only two pages, and serves mainly as an introduction to the rest of the book.
The next section is focused on player options, starting with two new themes. The Brute (+Str) is good at treating deadly wounds, using improvised or nonproficient weapons, and staying conscious after they've taken damage, while the Rogue (+Cha) is good at changing attitudes, using skills they haven't trained in, and finding friends.
Following this are three new archetypes - which, remember, can be taken by pretty much any character. (Of course, some character idea work MUCH better for a given archetype than others.) These include the Boarder (who's good at taking advantage of cover even when they're not behind it), the Gunner (who excels at hitting fast and hard with ranged attacks), and the Senior Officer (who support allies).
That's not the extent of the added options here, though. We also get new options for the Mechanic (like an Assassination Drone chassis), the Mystic (mainly the Destroyer Mystic Connection, which is as violent as you'd expect), and a spell for the Technomancer that turns vehicles invisible.
The third major section (yeah, that was all part two) is about Pirate Loot, and covers new general equipment, melee weapons, small arms, and even starship equipment that pirates might like to have. Some of these are pretty nasty tricks to use against players - or to have players use against others! - so GM's should be careful about what special technologies players are given access to. There are also two new starships: boarding shuttles and gunships, which aren't very impressive solo but could be rather nasty in larger numbers.
The fourth main section focuses on NPCs. Now, as the publisher was quick to point out, the full rules for making NPCs hadn't been released at the time this was published, so the various characters appearing here might not be quite 'by the book' as allies or opponents. Still, they should be perfectly usable, and players probably aren't going to notice a difference.
The last section is a 'neutral' zone friendly to pirates. Known as 8-Pieces Port, this is pretty easy to drag-and-drop into any campaign as a site players can visit. Each of the sections of the port is given a one-page writeup, describing the demographics, notable locations, and general personality of that area. Several rumors (i.e. potential plots) round out the section.
Overall, I feel this is a pretty solid supplement. Now, I'm not going to attest to any mechanical excellence in the rules, because Starfinder literally came out on the day I wrote this, and I haven't had time to digest its math and systems yet. Nevertheless, I feel like this is a pretty solid product, and an excellent option for any GM who wants to add a little (or a lot) of space pirate flavor to a Starfinder game.