TOS - I look upon with fond childhood memories. Probably what sticks with me the most is the Spock/Bones dynamic.
TNG - The Federation statesmen travelling around the quadrant, building new/stronger relations with other races.
DS9 - Darker, grittier, complex, brilliant.
VOY - Seven, Borg, Seven, Holograms, Seven, Janeway, Seven. Nice idea, badly executed.
ENT - Nice idea, badly executed again--only this time with gazelles.
NuTrek - So long as I don't think about lens flares, emotionally unstable NuSpock, terrible NuUhura, rehashed scripts, supertransporters, megawarp, mammoth starships, then its ok to watch in small doses.