For me Black Lagoon and Cowboy Bebop are two of my favorite series. The mixture of interesting and human characters, excellent (if over the top) fighting, and underlying and hidden discussions and opinions about life, people, etc. When I first started watching Black Lagoon I fell completely in love with the characters, the differing points of view conflicting, the psychosis, the struggles to understand each other and dealing with a wide variety of backgrounds and histories. And to top it all of was that they felt real and believable. Characters didn't just do things because the story needed them to, but because its what they would do based on their particular ethos.
The OVA felt like none of that. Well a lot less of that. Minor character spoilers ahead nothing particularly story related.
My biggest issue was that Rock suddenly seemed to jump off the deep end. In the beginning of the OVA he is still the same person from the series, trying to stand amongst the gangsters and murderers of Roanapur and trying to be a player in things, while still trying to hold on to his morals and ideals from his life as a salary man. Then he just suddenly switches to a mastermind role who has everything in his pocket and in several shots in the OVA is portrayed almost as a villain. Nothing wrong with the concept of an evil protagonist, Black Lagoon is full of them, but the change in Rock is so complete and he shows none of his usual motivations, is he doing this because of what happened in Tokyo in the last season? Is this to try and spite Chang? Or has he just suddenly snapped and dropped his previous ideals? They bring up what happened in Tokyo for a bit at the start and then it's never mentioned or alluded to during Rock's scheming. While the reasoning they provided at the end feels sort of hollow and pointless.
Apart from that Balalaika lost a lot of her bite and felt like a girl raging at the wind, none of her usual "I'll do what you want but I'm going to make sure it costs you". Chang went from being a sort of suave gunman, who had a sense of humor hiding the power and darkness he posses, to a character who just sort of sat in a penthouse smoking and looking pensively at things. Even Revy seemed to be like she was trying to redeem herself and let her ideals be easily run over. It felt like a different Revy than the one in the submarine or in Tokyo.
The main character was also a bit ambiguous. Following Rock at first, viewing the scenario from his point of view, to sort of abandoning him and following Garcia and Fabiola viewing Rock as evil or at least malicious.
This isn't to say that it's a bad series, the gun play is still excellent (and over the top), some of the dialogue and scenes are great. It also provides some good back story (although it didn't really do anything with it as a lot of it is revealed towards the end of the arc and it doesn't feel like the revelations have any impact on the story).
This feels like Black Lagoon light (ironic considering the added violence and sexuality, a good visceral addition that I would love to see more of in the series) the characters just weren't there.
Having the story drive the characters rather than the characters driving the story makes for an exciting series, but one that lacks the usual depth and intrigue of the regular series.