Everything the movie did well:
-Pretty good plot and protagonist.
-Really cool action and sets.
-Really good cast of actors.

Everything the movie did bad:
-Lots of pacing issues, it feels like this movie's plot would bave worked far better as a show rather than a movie.
-Not the most unique plot.

Reasons for the movie's strengths:
The cast was selected very carefully. The special effects director Nobuo Yajima had experience in Super Sentai and Ultraman allowing to do the giant scenes in J properly.

Reasons for the movie's problems:
The movie's production was temporally halted because it the staff weren't allowed to release a movie in January like they originally intended and was only allowed to resume production when they secured being able to do released in April of next year. This resulted in the movie being filmed in just 20 days.
Creator Shotaro Ishinomori and director Keita Amemiya didn't want to have a Giant rider, and the idea was implemented alongside the movie's name in the very last draft of the script.

Overall:
Pretty good film overall but not particularly great, the pacing drags it down significantly and feels like the movie isn't able to make the most use of its concepts. It's not a must-see movie by any means but if you're really into Kamen Rider I would recommend it still since it doesn't do anything offensively bad and it's still a good time overall.