Wow and here I though I was pretty negative.
Anyways, according to what little info I've found on message boards, the setting for Valkyrie Drive does have a lot of potential beyond the lesbian fest.
So we have the Exsters and the Liberators present on -Mermaid-, Siren follows the same concept but it adds an hybrid class on the form of the setting's antagonist. Being an Hybrid she can either wield an exster or becoming one.
The interesting thing is that Bhikkhuni's cast is composed entirely by hybrids. Beyond being a gameplay commodity (having the characters locked on a role would hurt the game) it sets an interesting twist on the setting. Bhikkhuni's island is the one where the girls infected with the virus learn to harness its power, Siren is depicted as being almost a concentration site and Mermaid is the only one to be considered "normal" until Mirei's arrival.
If the series does get a continuation where every character gets to meet, is gonna be very interesting to see how they react to each other.