The story is not amazing. There's just one minor mystery which was obvious from the start and had pretty poor argumentation and logic behind it contrary to the rest of the anime. This was probably done for the sake of fanservice but it felt like poor taste.
The characters are the same AS LONG AS you keep the end of episode 11 in mind when looking at Houtarou. There's some minor character development for him but not enough to warrant watching this OVA if that's all you'd be watching it for.
The animation and sound are the same as in the main anime. The animation remains conservative, even though the OVA can probably be labeled as fanservice, which is nice since the main anime was also like that.
Overall the OVA is best watching in context or with context in mind. It doesn't add a lot to the anime but it can be fun to watch if you like the anime.
