After finishing the summer movie, final stage and series itself, I can see why this was highly praised.

Kamen Rider Build is excellent at "show not tell". Combining old traits of the Showa riders (experimentation) and the new with Greek mythology being used. The strongest is the storyline itself. Everyone has a role to play, concepts not being taken out or in last minute. Also teaches you about thinking ahead!
While the tropes used for Sento and Banjou are VERY COMMON, they are a PERFECT MATCH INDEED!