Recs.
Updated
One of the oldest space RPGs - Traveller has a rich history and tries to recreate the feeling of classic sci-fi literature. Humanity has colonised the galaxy on an immense scale, and there is conflict and adventure in every corner and nook of space.
Specs
Pros
Pro It's actually science fiction
No magic, no fantasy conventions. This is actually science fiction.
Pro Diversity in setting and thematic complexity
Traveller is one of the oldest science fiction roleplaying games, and has a default setting that is even older. As such, there is a lot of cumulative depth that has been developed over the years. The current version of the rules (Mongoose Traveller 2nd edition) is very accessible, however, and allows new players to approach the game without a heavy load of baggage. Anybody who has seen an episode of Firefly, or any other typical space travelling fiction, will immediately understand the tropes. From the basis of its simple system, lots of interesting sci-fi ideas can be developed and there is a lot of material to use as inspiration.
Pro Adaptable
Thanks to various reference materials over the years, and numerous updates, it is possible to run almost any science fiction setting you want, from 1970's space opera, to cyberpunk and transhuman games (thanks to settings like Mindjammer and the addition of cybernetics in recent editions).
Pro Games-within-a-game
Traveller was, arguably, the original 'tool box' game, utilizing tables, dicerolling and design judgment, to generate things such as aliens, planets, star systems, economies, weapons, vehicles, spacecraft and characters. Character generation is a unique experience of taking risks to develop a lifepath history through career development. A bad roll could lead to unfortunate events, injury, prison or even death, while good rolls can lead to boons in skills, resources, contacts and reputation. It's actually fun to generate characters before you even begin play.
Pro Makes complex concepts easy
Starship combat can be a bear in many games. The current incarnation of Traveller has reduced it to a simple, fast, and easy to use game within the game that makes for fun and realistic (enough) game play that doesn't take away from the experience. The vehicle combat system and other rules subsystems work equally well. None are perfect but they enhance the flow of a good game which is what most players want more than anything.
Cons
Con Retro future basis can get in the way
It's 1970's sci-fi. So some unexpected modern motifs aren't well represented (transhumanism, wireless tech, internet, etc). There are, in modern editions of the game, plenty of examples of these, however.
Recommendations
Comments
Flagged Pros + Cons
Pro Adaptable
Thanks to various reference materials over the years, and numerous updates, it is possible to run almost any science fiction setting you want, from 1970's space opera, to cyberpunk and transhuman games (thanks to settings like Mindjammer and the addition of cybernetics in recent editions)