Traveller is one of the founding pillars of which RPG's have been built upon.
Even the cover harkens back to the old periodical sized books from GDW, so many years ago. Not that I ever got into Traveller, but I thought this was a great way to be introduced to it. The definition of game terms was very handy for understanding the facets of the Traveller universe. That being said, do not mistake the amount of information for an immediately playable setting. Much information is presented, but it is not very cohesive.