As always, I won't talk very much about the story. But I will say that this story is absolutely wonderful. While not too deep it still shows off much of the complexities that were touched on in earlier in the series.
Wonderfully done and amazingly fluid. This OVA really shows off the animation team's skill. Everything from blades shattering to a man getting a knife to the crotch is animated with wonderful quality.
Voice acting was wonderfully done, sound effects were great and the music was amazing. My only complaint is that some of the sound effects, while well done, were not as (for lack of better words) "Powerful" as they should have been for many of the things going on on screen. Such as a building collapsing. For a normal anime the sound would be a 10 out of 10, but given the quality of other aspects of this anime I'm going to be a bit more picky than usually.
The character design for Black Lagoon as a whole is one of my favorites, but some of the new characters are ****ing awesome. Especially the little maid. Character development is good too. As always the character development of Rock is top notch.
Overall this is easily one of my top ten anime of all time. I spent half the time I was watching this anime thinking "oh shit! That was badass!" If you like action and great character development this anime is for you.