So I just binged through this series today. Had been avoiding it for a long time since I have no interest in the in-your-face fanservices, but to my pleasant surprise, VD actually has some substance in it.
There are real lesbians, not just straight-girls-making-out-for-plot-reason. Mirei's attraction for Mamori was handled so well. So much so that I couldn't remember the last time I've seen a canon yuri romance being developed with such grace. It didn't feel rushed, Mirei's sympathy for Mamori just gradually changed into adoration and then full on romantic in a natural way. This is IMO thanked to 1) the excellent pacing of the show and 2) the tasteful execution of jealousy + protectiveness moments.
The OP and ED music actually sound good. I didn't skip a single OP for all 12 episodes, something I hadn't done in years.
The final battle was awesome. The weapons and Mirei's Valkyrie form all have great designs.
Most the characters, including the villains, are likable. While they're not the most multidimensional characters out there, they do exhibit some degrees of well-roundedness instead of boring archetypes.
My only griefs with this show is 1) the fact it's a softcore porn (The oversized breasts make some of the girls look less pretty than they actually are. The bare tits/butts/crotches, tentacle scene, undignified crude poses, etc. make the show look cheap and hard to respect) and 2) some of the plot points are lazy asspull (pretending to be a guy because "it will guarantee you to be a leader among girls", really??? Going batshit insane because you're being used as a lab rat, sure, but why not getting angry when they first turned you into a living weapon as well?)
Tl;dr: expecting dumb porn, got a decent action show with real romance instead - as long as you can tune out the porn parts.