The characters mostly. A combination of the writing and acting. I don’t dislike them (mostly) but I don’t feel in my feelings as compelled by Data’s journey for humanity as I do by the Doctor’s, for example.

Also the interior of the Enterprise-D is kind of hideous to me. Not that it’s a huge factor, but I like the softer lighting of Voyager or the NX. Even DS9’s intentional ugliness wraps around and I find it comfy. The Enterprise-D just looks like a garish 80s hotel.