Traveller to me (by which I mean Books 1-3, and maybe Starter Traveller) is a classic, a perennial along the lines of Monopoly and Diplomacy, if not chess and poker. The combination of simplicity and limitless potential in those original LBBs is astounding -- I was looking through them last night for the first time in ages (I normally use MT and/or The Traveller Book) and was newly amazed at how fresh and inspiring they remain even today. Sure some of the rules are inefficient and the technology is all dated and feels like the 1970s (or even the '60s or '50s) in space, but that's not really a problem -- most other sf of the period feels exactly the same way, and in a way it helps emphasize that Traveller is fundamentally supposed to be about people and interactions, not gadgets.
For actual play I still prefer MT because I like the advanced/improved rules and don't mind the extra complication, but there's something that's just so unassumingly appealing and primal about the simplicity of the original rules -- the entire Universe in 144 pages, no need to every buy anything else! -- that can't be beaten. Only the original (3 volume white-box) D&D even comes close (and is therefore, non-coincidentally, the only other rpg I'd grant Perennial status to). I think that GDW made a big mistake when they took Traveller out of print upon releasing MT (just like I think TSR made a mistake taking white-box D&D out of print when they released AD&D) and am glad that FFE has brought it back to take its rightful place in the pantheon of classic, perennial games.
Regarding which, FFE000 (Books 1-3 in a single 160pp perfectbound volume for $12) seems to only be available with GRiP or direct from QLI, which is a real shame. This book should be widely distributed to game, hobby, and comics stores (including those that don't normally sell rpgs), bookstores, newsagents, heck I'd like to see it at groceries alongside the dice and card-decks!