TOS - Cheesy, daring, awful and inspired by turns: a gloriously chaotic juxtaposition of high concept and lowbrow elements, progressive aspirations and unabashed chauvinism. Amazingly evocative on a shoestring budget, Trek at its freest and most charming notwithstanding Kirk's gradually-rising Marty Stu count and Spock's tendency to spontaneously manifest plot-motivated superpowers.
(The TOS movies - Leaving aside the curiously inert TMP and the disaster of The Final Frontier, these were mostly broken by cloying, setting-smothering sentimentalism, save for The Wrath of Khan
which provided a nearly pitch-perfect take on theme of advancing age and its effect on the perspective of the adventurer. If only they'd stopped there.)
TNG - Trek on a more blandly even keel, with less cheese but less daring, bigger budgets but less integrity. Drenched the heroes in the pretentious self-satisfaction of utopian ambassadors to the primitives, a disastrous idea that would permanently hobble the Nineties franchise henceforth; but had some fresh dramatic ideas and moments of real excellence to compensate for the too-safe second-hand feel.
(The TNG movies - varying degrees of awful, even at their best showing a curious refusal to build, explicitly or tacitly, on the seven seasons' worth of character work and development that should have been their greatest strength.)
DS9 - The weight and weariness of Continuity is starting to show; to compensate DS9 is forced to venture right out of the action-adventure box and into attempting straight-ahead drama. The results are mixed, at points quite impressive but not consistent enough... and another, fresher franchise has come along in the form of Babylon 5
. DS9 is finally forced to imitate, in inferior fashion, the new franchise's interstellar war arc and resort to stunt-casting to stay afloat.
VOY - The launch into the Delta Quadrant can't mask that this a tack back into safe, staid Trek territory. A wasted opportunity mainly notable for featuring the most egregious instance of stunt-casting-for-tits in all of Trek.
ENT - The show-that-must-not-be-named. Another potentially daring shift of setting too timid to venture outside the straitjackets of the existing Trek style. John Billingsley and Jolene Blalock are wasted opposite an underdrawn human cast tepidly conceived as backwoods avatars of Earth's Sensawunda. The first time watching Trek felt like work. I'm told it got better in the third season but I'm afraid they lost me so definitively in the first season that I'll probably never know.
NuTrek - The Trek universe rebooted with its cartoonish elements dialled up to eleven, a Starfleet curiously reminiscent of the Improbably Powerful Student Council manga trope, and characters transfigured into full-on comic book heroes with Kirk's Marty Stu count now through the roof and into orbit. Some thrilling set-pieces and ace visuals, the infamous lens flare notwithstanding, and some good character ideas within the limits of the concept, but the stories don't make a lick of sense even on their own terms and are so broken that by the end of Movie Two the writers have -- probably unwittingly -- literally rendered both death and starships superfluous in the setting.
On the upside, they've revived popular interest in TOS, and since Starfleet is no longer needed in the "alternate timeline" perhaps we can safely give the rest of that a miss and stage a full-on return to Trek's roots. I like to think there are always... possibilities.