Series Better anniversary, but still bad
My score for the series is probably 6/10. It had some high point, it is better than the last anniversary series, but ultimately it has more bad than good points.
Design : Most of the rider costumes are okay (Ginga is a bit too bulky for my taste), even Grand Zi-O grows on me. Another Rider probably had the best monster designs for the entire Kamen Rider series. Tsukuyomi is my favorite female rider designs ever. Not too fond of Zi-O armor, but they are unique at least, I'll give you that. I absolutely love Oma Zi-O design.
Plot : For anniversary, they had some of the best arcs (Agito and Blade came too mind). But then they failed at some, like Kiva arcs, nonexistent Double arc, and that rehash-with-too-much-drama-of-what-is-supposedly-Drive-arc. I am kinda pissed off at the last one.
Zi-O's original plot is really messy though : They even forget Zi-O 2 could rewind time, or that Geiz Revive supposed to kill him, what the heck. Do they ever explained what is the deal with Kikai all about? Sougo had the power of creating future Kamen Rider through dreams? Given what happened in Over Quartzer, is Zero One basically Sougo's dream too?
Characters : Early on, the notable character is only Woz and Decade. Early Geiz is horribly tsundere and keep switching between killing Sougo or not; people actually believed Tsukuyomi trying to kill child Sougo, Sougo himself didn't have much character development focus.
Villains : And this is where the series really fell flat. Timejacker felt like useless villains that is only useful for creating Another Rider of the week. I get Heure and Ora are stupid manipulated by Swartz, but Swartz himself isn't a good villain. Tsukuyomi's basically pulling Ora 2.0 and he believed her? Not to mention when Sougo asked his younger self what he would do and he just revealed his evil plan - seriously who wrote this thing?
I know I kinda complained a lot, the series isn't actually that bad but I can't see myself rewatch it again. I am somewhat glad there's no actual crossover for Zero One. Reiwa era should start on a clean slate.
Series More like Decade S2.
This series is not bad though, but still it's far from perfect in the eyes of other Kamen Rider fans, even myself. Despite living up to the expectation as commemorating the 20 years of the Heisei Kamen Rider series, it still has many, if not all, downsides as to expect.
Design: I have no complaints for the Riders' suit designs with little to no asymmetrical design, including Geiz Revive, Woz Ginga, and even Grand Zi-O. The Another Riders live up to the main Riders they are based on, giving us the reflection of what would be that Rider like if it became a weapon of evil, a reference to the Cross of Fire that was mentioned in Wizard.
Plot: For a second there, though combining Den-O's time travel theme and Decade being the anniversary Rider who uses his predecessors' Rider powers as his own. Some of the arcs don't live to its expectations (i.e., Kiva not only due to the lack of the said Rider's involvement, instead we get an alien from a meteorite attempting to destroy the world; this is due to the fact that Toshiki Inoue of all people is the one writing those episodes). Shinichiro Shirakura elaborating plot points is not what you see in the past series. And this is why I'm not very fond of him. Lastly, my obvious complaint for the season is being Decade stealing the spotlight.
Characters: The only notable characters I'm grown up to is Woz, the OG Black Woz. Geiz going from "attempting-to-kill-Sougo to friends-with-Sougo and siding with White Woz to attempt on Sougo's life again and so on" kinda messed up the Second Rider trope where they start as anti-heroic foils to the protagonist before becoming close allies. Tsukuyomi, before her past is explored, lacks, if not entirely, 3-dimensional characterization than past female leads. And to quote troper readrunners' review: "Sougo himself didn't have much character development focus."
Villains: The Timejackers have no backstory of their own, save for Swartz. Heure and Ora spent most of their time as Swartz's errand boy and girl until they come to realize it in the endgame arc. Swartz isn't a very enjoyable villain either, and is much less of a fighter compared to past villains. Oma Zi-O's characterization is somewhat questionable once we found out his true intentions are. We thought this guy could be a heartless tyrant, or a fallen hero turned tyrant like Superman, but deep down he's actually trying to preserve his ambition as a king through present Sougo. In the end, he's pulling a Takumi Katsuragi 2.0.
Well, despite the flaws I've elaborated. It's been a sweet ride and Zi-O fills in as a fitting sendoff to the Heisei Era. Now with Zero-One coming soon, I bet the Reiwa Kamen Rider series should start anew with different trend that makes the new era of Kamen Rider differ itself from the Heisei Era. My overall rating for this series is a 7.5/10.