I think Invincible is the most underated album of all time, by any artist - period.
The thing is, with an album of that many songs, people are going to have their 'favourites' and there 'non-favourites'. There is nothing wrong with that. But to suggest that MJ would have put 'poor' tracks on any of his albums niave in my view. Some people may not like them on a personal level, but that doesn't make them 'bad' tracks.
In the right time period, with less distractions and problems in MJ's life, this album would have been huge! At least it will always be around for more and more people to gradually appreciate - which, in my view, they will.
Quality album from a quality artist.