Everything the movie did well:
-Likeable cast overall.
-Really great practical effects thoughout the whole movie.
-Doras feels properly menacing throughout the whole movie.
-Really cool action.
-Some pretty cool stop-motion.
-The villains feel properly creepy.
-Pretty good plot.

Everything the movie did bad:
-Not really that unique of a story.

Reasons for the movie's strengths:
Despite the movie having ton of production issues, like it originally being made with an adult audience in mind, being a sequel to Shin Kamen Rider Prologue that also crossovered with other seasons. Then became a kid's movie due to Toei having a poor fiscal year, it was still going to celebrate the 20 year anniversary of the franchise, even becoming the movie's namesake, but it ended up not releasing on the 20 year anniversary removing its crossover aspects. Then the original draft by producer Shotaro Ishinomori was rejected due to budget since it was too ambitious. Then the movie was triple-billed with both Gosei Sentai Dairanger: The Movie and
Tokusou Robo Janperson: The Movie, reducing the movie's length was originally planned to be 90 minutes.
But in spite the poor odds, the producers managed to amass an amazing staff due to collaborating with other groups from Toei. The directing of Keita Amemiya and the creativity from the staff allowed them to do more with less, resulting in a overall really great movie.

Reasons for the movie's problems:
Them not being able to follow Ishinomori's original draft affected the movie not being that original. But the movie doesn't do anything particularly bad, it just doesn't do anything to be considered a top-tier movie.

Overall:
Really great movie with good pacing, action and characters. This also feels like a perfect entry-point for anyone that wants to get into the franchise since it's not a 40+ episode show and it's a fun time overall. Overall high recommend to anyone who wants to get into the franchise, anyone who's into action movies and to Kamen Rider fans.