Pretty good but also pretty bad adaptation. The story is essentially original as it's not part of the original VN. The story being changed or converted when adapting a VN is not weird, like in Kanojo x Kanojo x Kanojo, Aneimo2 or Resort Boin, to say some of my all time favorites that changed the story to make it more cinematic. In this case, the situation we see in the OVA is not impossible though, it's more like it didn't had the chance to happen. The characters are pretty much the same and don't feel any incongruences between the original VN and the original story for theOVA, only the main heroine had her villainism buffed and the protagonist may or may not have different motivations (it depends on perspective).

The animation is soft and fluid, it's comfortable to look at and aged pretty well... Except for the scenes when they shadowed the characters in an already dark location to add more "mystery/drama" to the scene, that looks awful.

A problem in specific I have (more like a thorn than anything else) is the mix of flashback/flashforward story telling they use, I FREAKING HATE THAT. Showing the end and then saying "And this is how it happened" is something I hate and always will.

The story, animation and scene direction are pretty good, only the the jumping between before and after is bad.