I had the same thought as well.
Seriously. We have the young ignorant kid given a power he knows nothing about and unwillingly thrown into a war. (Guyver 1/Amazon Omega)
We have the powerful formerly aligned with the big enemy character who is really in this war for his own goals and just uses the ignorant kid as a tool to get his way. Constantly threatens him while he is at it. (Guyver 3/Amazon Alpha)
The monsters are artificially made by a big corporation. (Cronos/whatever the company's name is in Amazons)
The enemy grunts are monsters who hide among normal people. (Zoanoids/Amazons)
The Riders are reminiscent of the Guyver units. Kid keeps discovering new abilities left and right. He also seems to "lose control" for various reasons often. Alpha is a mirror to Guyver III. Knows his power and how to use it. Sigma is similar to characters like Guyver II for obvious reasons, sans having a glaring weakness of some kind. And similar to other characters like Guyot/ZX-Tole as he was resurrected from the dead and stronger than ever before.
There are other parallels too but I am half awake. Guyver in of itself is a homage to Kamen Rider in of itself.