Everything the show did well:
-Every character in the hero cast is likeable and useful.
-Villains are menacing and feel like a real threat.
-Consistently amazing action and stunts.
-Properly ups the stakes with each following arc.
-Solid world-building.
-Great balance between a light cop J-Drama, slice of life, tokusatsu action and horror from lovecraftian-like serial killers.
-One of the best final fights in the franchise.
-One of the best power systems in the franchise. Godai has all his powers from the beginning but doesn't know how to use them due to getting them with no context, having him to practice his powers and his friends to decipher glyphs explaining the lore and the powers of the arcle to properly know how to use them
-The world has a more 'real' feel than other rider shows.
-The cops manage to continously feel useful and keep up with Kuuga despite him being the only one with transformation powers.
-The cop partner relationship of Ichijou and Godai is really well done.
-Has good re-watch value due to the main villains having a different language.
-Better acting than most rider shows.

Everything the show did bad:
Honestly most of these are nitpicks.
-Due to wanting to make a lovecraftian villain that the viewer cannot properly understand, the main villain feels kind of plain as most of the destruction he causes happens off-screen and doesn't get a proper character. But despite this flaws he feels properly menacing.
-The shift from normal J-drama stuff to hardcore murder done by tribal monsters can be jarring at times. Especially in the Jean/Enokida episodes.
-The CGI feels really dated, but it is used sparingly and honestly CGI pretty much always looks bad on Toei's mainline toku with the exception of Hibiki, kinda King-Ohger and seemingly the upcoming rider show Gavv?
-The show being shot differently from any Toei toku which can feel alienating for toku fans but it's not really a bad thing just different.
-Having multiple scenes where you don't know what the characters are saying can be tiring for some viewers.

Reasons for the show strenghts:
Kamen Rider creator before passing on wanted to make this show unlike any that preceded it. Ishinomori production recommended producer Shigenori Takatera to do so as well. This along a bunch of other factors resulted in this unique setting. Takatera and director Ishida really wanted actor Joe Odagiri to be Kuuga, and went with a more J-drama approach to its direction since it was what he preferred. Producer Takatera ideas often clashed with Takeyuki Suzuki's ideas but they ultimately managed to have a good balance of both. There's more factors but it would be to many to list, but overall Kuuga had a way different approach to previous shows and slightly more budget than usual which lead to the show being as great as it was.

Reasons for the show flaws:
The main writer Arakawa wanted to keep the details of the main antagonist vague in order to make him creepier, he succeeded in making him menacing but makes him a more boring antagonist when compared to other villains in the franchise.

Overall:
While not my personal favorite, I feel that this is objectively the closest to a perfect rider show. It just doesn't have any big issues. I would recommend the show to pretty much any Toku fan or even a cop drama fan that has never watched tokusatsu, since it's pretty much a cop drama with superpowers. I could only see people not enjoying this show if they really despise a genki-type protagonist and the flow of a cop dramas.