The Incredibles left some massive footprints to fill, and the sequel filled them excellently. If you like the first movie, you should definitely watch the sequel. (And if you haven’t watched the first movie, you should watch both.)
Apart from the issue of the movie being somewhat inaccessible for people with photosensitivity issues, my only negative criticism is that the pacing was a little slow in the beginning. But the slow bits were essential and it does result in a good sense of building tension, so it’s not a huge issue.
The plot was engaging (if a bit muddied by a lot of subplots, though those were individually good as well), and the fights creative and well-choreographed. While the main plot had some basic similarities to the first movie, it was different enough to not feel like a rehash.
This movie is an excellent example of good sequel-making – it does something new with the original premise and expands on themes and elements from the original. It picks up things that were given less focus in the first movie and elaborates on them, without losing touch with the core themes.
So in summary: Good movie, excellent sequel, 9.5/10 stars!