There's something striking about this two-parter. It is ridiculous, overblown, and rather... ...dumb.
Berman, Braga and the rest of Paramount made some serious errors in implementing ENT, no doubt about it. They failed to recognize that, by going back to the "beginning", they were unraveling alot of assumptions regarding what the STAR TREK Universe was about; they were literally re-inventing the wheel, only they treated it like it was a prequel to TNG. This much is obvious. And then they got the bright idea to throw a dollop of TOS on top of it. Actually, as silly as it was, it was an entertaining flight of fancy. Much moreso than VOY.
The episode ditches strumming guitar earnest tones of "Long road" (the most despised opening music in all of Trek) and replaces it with macho sounding fare with dynamic military images in the background. Things go bang! Indeed, the two-parter is filled with a lot of pew-pew! action and the characters are simple and action-oriented.
I do not understand your hostility for the theme music. Maybe it's just me, but I actually thought Russell Watson's song sounded grown-up and one of Berman's best attempts to articulate the ideals of TOS, setting it to music and embedding it in every episode.
It seemed to be a refreshingly creative way to bring the old "Space, the final frontier..." theme narration into 21st-century TV format. I thought it worked very well.
The whole point of ENT, as I understood it, was that these characters, and Earth overall, had evolved technologically and were in the process of stepping into their own future (deep space flight, the Coalition/Federation, high-tech prosperity, etc.) but those characters and their society still had alot more in common with you and I than we saw in any other TREK.
As for the gratuitous explosions and nasty action and infighting exhibited in "Darkly", that's to be expected. It was the final entry in a long list of Bermanian treks that tried to capitalize on "Mirror, Mirror". The only one of these alterniverse shows to ever impress me was "Yesterday's Enterprise", and they never followed up on that one.
The episode feel like a critique of fan-service, even as much as it caters to it. It functions as a guilty pleasure, but clearly does not aspire to be anything more than a guilty pleasure. This was fun as a change of pace, but you couldn't sustain a series with dialogue.
Enterprise failed, but this episode seems like the series making a case for its own virtues. Sure, Archer is stupidly earnest and plucky (like an oversized human version of his Beagle), but consider what might have been... ...surely plucky Archer is better than the MacBeth version? If so, we might be inclined to reappraise the virtues of the regular show.
I agree that ENT had many things about it that were controversial with longtime TREK fans, and that it could've been better-implemented. Having said that, how many TV shows do you know of that stay on the air for four consecutive years that are branded a failure?
If ENT in general and "Darkly" in particular left a bad taste in anyone's mouth, it's probably because (1: the show's makers were obviously running out of ideas; IIRC, Berman himself thought Paramount should not do ENT... (2: While ENT had some great story ideas like "First Flight", the overall lack of a creative direction with the show was getting pretty obvious, probably contributing to problem #1... (3: Hollywood, being silly as it is, recognized that Berman's shows had strayed too far from what TOS was all about, so naturally they sought to compensate by dumping the Starship Defiant into our laps; problem solved, or so they thought.
"Darkly" was fun, ENT had potential, Archer (and Bakula) were pretty good as the captain of the Starship Enterprise. But just like your Daddy's T-bird, you aren't gonna have much fun with this cruiser if you don't put any gas in the tank and you don't have a destination to drive to. At least "Darkly" was a fun little jaunt to the hamburger drive-in for a couple Saturdays. Just don't expect Brenda to fall in love with you over it.