I'm curious how everyone thinks about the different series - which things come to your mind - other than the characters, obviously - as being particularly integral to this series rather than that one.
TOS is Spaceships, First Contacts, Alternate earths, Energy beings, Klingons (but only if the movies count), redshirts, alien fist fights, time travel and Robots
TNG is the Prime Directive, the Holodeck, Q, the Borg, el-aurians, Androids, Romulans, diplomacy and colonies
DS9 is Cardassians, Bajorans, Ferengi, the Dominion War, the Prophets, long running story arcs, Section 31, runabouts and regular people
Voy is the delta quadrant, transwarp, the Hirogen, 8472
Ent is xenophobia, history and nostalgia
Maybe I'll be able to think of more later, but I hope that should get things started.