OVA's are judged based on their parent anime because customarily they lack the screen time to create a new story or experience, characters don't undergo any vast changes, and there are no fulcrum point events that a series rests upon.
In the Hyouka OVA, the audience is given insight into what happens between episodes 11 and 12 of the parent anime. Although there is nothing ground breaking to be found in this OVA, if you enjoyed any aspect of Hyouka, you will assuredly enjoy this OVA.
The OVA fits in perfectly with the rest of the series. Its animation is top notch, the sound is superb, the characters interact as they should, and it is definitely enjoyable. If there was to be a question brought up regarding this OVA, it would be, "Why wasn't this OVA just included in the parent anime?".
For those that enjoyed Hyouka, I highly recommend this OVA to you with an 8/10 rating. You might just find yourself to be "curious".
