It’s not even about the database per se… what’s not easily replicated are the annotated (commented/analyzed) games, high quality metadata.
This actual software, in terms of UI, is basically shit, and the technology is questionable (search really should be an order faster - my understanding is it has to do a full sequential read of the main DB (which is several GB)
Oh, the software is absolutely awful, and you're spot on about the metadata (and the CBH format as a whole,) but I would also toss in another point where it's (sadly) the best: Opening prep. There just isn't much else that can compare despite the awful interface.
