Agito heavily features night battles, shadow play, and ominous overhead lighting. Low-quality encodes turn these scenes into a pixelated, muddy mess. High-bitrate extra quality releases preserve the deep blacks and shadow details.
It is important to note that Kamen Rider Agito has had a complicated history regarding official international releases. For many years, there was no official English distribution, leaving the preservation of the series entirely to the fan community. This has led to a fragmented landscape where multiple subtitle tracks exist, some re-translating older scripts to correct errors, and others creating entirely new localizations.
Be careful. Because Agito never got an official HD release (Toei hasn't given it the "Blu-ray Box" treatment yet, though it's rumored), most "HD" versions are fan-upscaled.
The Ultimate Guide to Experiencing Kamen Rider Agito in Extra Quality with English Subs
The foundation of an extra quality release is the source material.