The Incident has a lot of flaws, but the big one was that it felt pretty uninspired. If you look at the band's career, and how everything was leading up to The Incident, it's a bit of a shame. The previous albums had something special, but The Incident was a rehash of old ideas, and the most generic heaviness in terms of PT trying to be Djent or sounding like Meshuggah. In the end the album had some enjoyable stuff, it wasn't bad, but it just wasn't what everyone hoped for.
The bigger the ambition, the harder you will fall. And I think there are several reasons as for why people felt a bit lukewarm towards The Incident. First off you had the song-cycle concept which felt very epic, and one of those things "either they pull it off, or they won't". Then you have the information about the album before it came out, "its going to have sounds from all PT-albums, even the first" which gave people a lot of hope, because taking the best from all eras of PT sounded really interesting.
In the end it was just a decent album. In recent interviews, even Steven himself has given a vibe that he isn't completely happy with how it turned out, and maybe, just maybe that's the small reason of why PT might return. I don't think they will personally, because PT feels completely dead, but if there is anything that might be a reason for a PT-return, it would be so that they don't let The Incident be the final chapter of a great band. Again, it's not a horrible album, but it's still the last memory people will have of them.
And I probably agree that OTSOL is a more "fun" album to listen to, even though Incident has higher lows. On the other hand, those two albums shouldn't even need to be compared in the first place, given the fact that OTSOL was shit SW recorded at home and just goofing around. The fact that people even compare them says a lot about the general opinion on The Incident.