TOS: marriage of camp and 60s idealism. Love all of Kirk's speeches--the origins of Trek's expository style--and the Spock/McCoy barbs. Earth-like planets, soft-focus women, deified computers, and noncorporeal beings--Trek staples.
TNG: Trek idealism gets a huge boost with classical acting, Sean Connery in command. Time shifts and tricks, deflector array solutions, Riker's creepy flirtations, cramped shuttlecraft. Anthropology and diplomacy. Got better as Rodenberry let go of the reins.
DS9: Pinnacle of Trek storytelling. Examined the premises of Trek idealism and gave it a backbone. Garakisms, Dukatisms, Weyounisms, Quarkisms. Sisko's voice getting lower, lower, lower. It's a fake! It's real! She's my mother! She's a wormhole alien! Punch through! Be gods! Lots of taking things to the extreme.
VOY: TNG part II. Janeway's bitch fit in Scorpion I. Implants. Holodeckin'. The lovely Sara Silverman. Too much complaining about leola root. Kim's bad Laforge imitation. UPN.
ENT: Ruined by Temporal Cold War. Captain needs to watch Q Who: space is tough. SHRAN (in all is Weyouney goodness)! Catfishin'. Pockets on the sleeves. Steampunk-style warp core. Contrived high warp transfer. Potentially of the Romulans. Real development of Vulcans. T'Pol's slow blink.
JJ-Trek: Proves why Sci-Fi and comics should remain separate. Looks pretty. Ruined by temporal concept. Reworked tunic. Shields that seem to do nothing. Underthere! Sisyphus in the warp core.