I have always found interesting how even though Kamen Rider and Super Sentai both used humanoid monster that display intellect, they both play in the oposite extremes of each other.
In KR the kaijins are true villains, they are smart evil bastards that want to kill/hurt/destroy other people, and some of them even have development of their own. Super sentai on the other hand has Kaijins whose portrayal is entirely campy, they might be intelligent but they don´t harm other because it brings them satisfaction, they do it because they are evil and that is their mission. I know that there are exceptions to these rules but this is how it has been in most of the series i have seen.
Older toku really had some interesting concepts for monsters, like in Robot Detective where every BAD robot has an unique ability that was always portrayed as an important part of the mystery behind the crimes. There were also the Destructoids from Kikaider, their designs were anything but subtle but i always find it interesting how whenever Kikaider trades punches with them you can hear a metallic clank, highlighting the fact that they are Androids.