Traveller is unlike either Vampire / World of Darkness or D&D.
Traveller character generation, for one thing, is very much unlike the above two games. Your characters' career up to the start of play is as important as the game itself. You can make Traveller chargen as adventure in itself.
D&D and World of Darkness characters enter play with a bunch of selected characteristics, Skills, Merits and other advantages, and gradually accumulate more characteristic/Skill /Merit points through XP expenditure. The Traveller character comes more or less equipped with all the skills he will ever have. He can improve his skills, but only with great effort: Traveller doesn't have an XP system.
In Traveller, also, the Travellers - while they may have come from certain careers - don't generally belong to those careers when play starts, other than Scouts (who remain Scouts-on-Detached-Duty until their sixties or until death) and Psions (who generally remain psionic until death).
In Vampire as in Werewolf, Mage, Changeling, Promethean, Hunter and Geist, a character belongs to his Clan/bloodline and his Covenant from the moment play starts, and remains an active member of that Clan / Covenant. The Clan, Bloodline and Covenant / Tribe / Path, Order and Legacy / Lineage and Refinement / court / cell, compact or conspiracy /Krewe play an important role in the character's development: in Traveller, your character only has loyalty towards his shipmates.
In D&D, characters progress through levels, learning feats and improving upon their abilities, including their ability to suck up damage: in Traveller, a character's health remains fixed: his physical characteristics, Str, Dex and End, determine how much damage he can take before dying. And Traveller characters do not have levels or feats.
Finally, while D&D focuses on the dungeon, and Vampire focuses on the Danse Macabre, Traveller can have any kind of focus, any kind of adventure: it all depends on what the Patron wants the crew to do, or on where the speculative trade die rolls lead. Do you want your characters to become privateers, to develop psionics, to explore strange new worlds or to rise to the position of Archduke and run an entire sector? Whatever your goals, the Referee has a story that will let that happen - or not.