TOS: The big three; Kirk, Bones, and Spock (and company). The beginning of a dream. A few good episodes but the movies was where they shined.
TNG: A slow start, through the eyes of exploring diplomats, Trek expanded. Factions are more defined. Through morals, duty, and honor, Star Trek's base was becoming more than an adventure.
DS9: A slower start, Trek expands again. Everyone isn't Ok with everyone else and sides are chosen. War-time space opera with more dynamic characters than before (Not Ezri). A darker (albeit needed) side of Trek.
Voy: An even slower start, the galaxy expands. The concept was great but not executed as good as it could have been. Characters aren't as dynamic but the crew were more of a family than ever. Back to alien of the week without the catching up on them later factor (Did Ocampa survive? Are the Malon still jerks after Voyager showed them a better way? What are the Hirogen up to?). An equal mix of good and bad. Trek loosing it's touch.
Ent: The end of that continuing mission feel. A loss of a lot of Trek quality (even the opening credit's music). Character are even less dynamic (some without any real back story). A few good episodes, the tie-in were the best (other than it's finally).
NuTrek: Character dynamics aren't as good as previous series though they only had two movies to build it. Not worried about Prime Trek revivability with the alternate reality route they took, and how Prime Spock didn't cease to exist. Back to action. Good for the movies, though if they make another series I'd rather it be in the Prime timeline. I liked Into Darkness as a homage movie though I hope part 3 is more original.