I gotta say, I found the story from the first OAV (OVA?) to be pretty good and enjoyable. It can get a bit dark and surreal at times, but I think it really made a difference in the 40 minute short. I found myself consistently trying to guess the next turn in the story and almost always refreshingly found myself wrong. One of the things I especially enjoyed was how they humanize and expose various characters throughout the series. For example, you only really get to see Ame's face for the first time within the last 5 minutes of the show, even though they introduced her at the very beginning. Later when they briefly hide her face again, it's done to a different effect. Very cool.
It's got all the standard elements of a short story: introduction, rising action, climax and conclusion. I'd be surprised if the second OAV was a continuation of the first.