This Data episode is a throwback that wouldn't be out of place amidst any of TNG's seven seasons. It's a vanilla concept that doesn't break any new ground (outside of being the rare medical mystery where the audience is ahead of the characters.) It is nonetheless well executed and mildly entertaining.
The B story is, surprisingly, not about the Enterprise crew trying to find Data (probably because Patrick Stewart was unavailable for most of the shoot) but it is instead about Riker giving Troi a command test. It's somewhat implausible and predictable, but short and inoffensive.