TLJ is the 8th movie of a 9 movie nonology. The previous 7 had a somewhat coherent storyline. The micro was about the Skywalker bloodlines and how it influenced the macro political scene. Zoom out to the 10,000 foot level and it's good (jedi) versus evil (sith). Zoom in moreso and there are political undertones, conflict of what constitutes good vs evil, and so forth. TFA introduced a new dynamic that somewhat deviated from the established storyline. However, it was nebulous enough that it could have been brought back into the main storyline. TLJ took that right off the tracks.
- Rey? Parented by nobodies. Uber-jedi with nil training. As pointed out ad-nauseam above, the ultimate Mary Sue.
- Snoke? Ultimate bad guy, force powers unforeseen until now. Able to manipulate the thoughts of Force-sensitive people. Pulled together the First Order. Destroyed the Republic. And .... killed off in the second movie by a ridiculous concept.
- Luke? From hero to zero in one film.
If it were a stand-alone film it wouldn't be bad. But as a component to a previously-established series, it's garbage. The question that many have is "Where does the 9th movie go from here?". And for some, the answer is "I don't really care".
If you liked it that's fine. But it's a difficult argument to make as to why it would be a good SW movie given all of its faults.