I was wrong. Kevin Crawford, the game's designer, explained that he decided to use the tried-and-true OD&D engine because it is so ubiquitous. Everybody that games knows what HPs are and how AC works, whether you like the systems or not. It isn't fully OD&D. It uses the Target20 method to-hit, and 2d6 for skill rolls. The Big Six stats are there in all their 3d6 glory. The bonuses range from -2 to +2. There are three classes, each with their own hit dice and experience table. All very familiar and comfortable. Which is the point: they are so ingrained in most gamers that these systems fade into the background without any effort.
The games greatest strength, aside from its prolific and talented designer, is its support for sandbox play. There are tables for randomly determining the barest details of alien worlds, such as atmosphere, size, biosphere, etc. There are also some tables that I'm not accustomed to seeing. There are extensive rules for generating Factions, and their operation. One of my favorite ideas here, though, are the guidelines for World Tags. These are just a simple sentence or two intended to almost immediately evoke something interesting about the world.
I've always enjoyed randomly determining star sectors and the rules for such are one of the make-or-break points in a sci-fi game for me. The problem I've always had, though, is coming up with unique worlds circling the randomly determined star systems. After a few solar systems I start running out of fresh ideas. These tags should definitely help with that. With these it will be easy to custom design key worlds in the sector and use the random tables for the rest.
There are complete rules for starship design and combat. There is also a supplement Skyward Steel covering naval architecture and warfare in greater detail. It isn't free, as are the rest of the things the links below point to. The pdf is only $9.99, though, and it is tightly focused on its topic, so it is definitely worth it if your campaign will feature naval themes.
All in all, this is a very good sci-fi RPG. There are many elements I haven't even mentioned, but by now there are many fine reviews. Besides which the pdf is free. If you're looking for a good sci-fi game that supports free-wheeling sandbox play, look no further.
SWN Free Edition
Everything you need. Period.
Infinite Stars
Formerly a free e-zine, now a blog. It covers more than just Stars Without Number.
Online Sector Generator
Generates a sector map, world index, NPCs, Corps, Politics, Religions, and Aliens. All with a single click of the mouse (ok, two clicks if you want to change the seed).
Mandate Archives
These free mini-supplements (about 8 pages in length) offer a very focused look at a specific campaign feature. They can be used as-is or tweaked to fit your individual campaign sector. The link points to one of the Archives, but links to the rest of them are found on that page.
Skyward Steel
Advanced rules for stellar naval operations and ship design.
