I got this one in print from a local store and was psyched to see that I could also get it in PDF! Let's talk about 2300 AD and why the Traveller system is a perfect match for it. Mongoose has done a great job of bringing this gem forward and it's a terrific purchase.
Now, I played 2300 AD back in the late 1980s/early 90s. It was created to be a bridge between Twilight 2000 - a post-limited-nuclear-war military adventure game set in the far future of the year 2000 - and Traveller - a far-future libertarian science fiction game in the Golden Age of SF style. It posits a world where still-recognizable nation-states colonize and vie for control over stars near Earth. No one-world government in 2300 AD, intrigues and politics make these first few steps into the universe fraught with adventure and danger.
The upside to Traveller has always been its flexibility - with its simple system you can be mercenaries, or on a diplomatic mission, or criminals and slimeballs. But it's been fairly rare to see a fully fleshed out campaign model for Traveller. Perhaps this is because it has always attracted the do-it-yourself mindset, just as the characters in the typical Traveller campaign scrimp and scrounge whatever they can to make their way in the universe.
However, 2300 AD gives a much more specific game world, fleshing out its universe in more detail. Instead of a vast galaxy, the characters will be visiting and coping with problems on only a couple of dozen nearby stars. Events on one will propagate and cause consequences throughout the game world. No longer will the most boring Traveller adventure outcome, "we fly away from everything we just did" be a feasible way to avoid the decision-and-consequence chain that makes RPGs and stories good. The universe is not that big in 2300 AD.
That's not to say that 2300 AD lacks flexibility. There are many pages of campaign structures and ideas, from military units to spies to explorers.
There are two areas that 2300 AD could improve in, one that is general to colonial games and one that is specific to this game. Specifically, 2300 AD could improve its usefulness in PDF form by providing pages specifically for player consumption - the hex maps are a great start here, but why not do what original Traveller did and have information about planets and colonies in a form that can simply be printed out and given to the players to consult just as their characters did? Instead, information that could be accessible to characters is jumbled in with commentary and side notes for the GM. Which is fine as far as it goes, but it limits the usefulness of the text for a Traveler group used to the classic "one paragraph entry in the computer book" style of deeply in-character play.
More generally, there are lots of games that have a colonial setup that pretty solidly fail to acknowledge the moral ambiguity (or even outright evils) of colonization. Even in 2300 AD, where there are a few other alien species in the "near" stars that are the target of Earthly nations' ambitions, there just isn't any mention that in certain circumstances the players are likely to be playing the bad guys. The game does a great job of setting up a situation that evokes the age of colonization and the rivalries that spread and changed during that time frame, but doesn't acknowledge that the modern player (hopefully) has a bit more awareness of the questions and problems raised by colonization over time. Also, do characters in this setting feel that way? Is this a political question at all? 2300 AD more or less skips this whole issue. So do many other games with colonial setups, so I guess it's no worse than them. However, I'd like to see games do better in this regard.
Those are really my only two critiques of the book . The simple Traveller system has been well-examined elsewhere so just trust me when I say 1) it's solid and 2) it's extremely extensible - you can pull in careers, equipment or even new aliens and locations from Traveler supplements if you like and have no systemic problems doing so. 2300 AD presents a remarkably complete game, including things like cybernetics, genetic modification, psionic abilities and a very thorough gazetteer that should keep you going for a long time.
The original GDW 2300 AD did a good job of showing the path between the postwar Twilight 2000 and the freedom-focused Traveller and what it would be like to mesh these two ideas. As a result 2300 AD was a vivid and exciting setting for adventure. Mongoose has preserved that core recipe (though it says that it no longer is related to the Original Traveller Universe in the introduction, the underlying concepts remain the same) and strengthened it with its updated Traveller system. The layout is good and the PDF doesn't have nonsense like background images to keep you from printing what you need. (There's a few odd diagrams and art pieces that suddenly pop into color here and there, but it's not harmful to the layout.)
I loved 2300 AD back when it first came out and I love it now!
[4 of 5 Stars!]