It's actually Z80-ish with some features missing and some new ones included. It's a Sharp LR35902 SoC with an SM83 core (not sure if it has been used in non-GB SoCs).
I can recommend The Ultimate Gameboy Talk for details on it (and much more).
https://m.youtube.com/watch?v=HyzD8pNlpwI
EDIT: I had the SoC and the core names the wrong way around. Thanks svendahlstrand.
Re:Choosing tools for Game Boy development
by svendahlstrand on Sunday January 30, 2022 @04:43AM
(#30135410)
I believe the LR35902 SoC is exclusive for the Game Boy, but the actual CPU core, SM83, is probably used elsewhere. Sharp's datasheets [2] mention home appliances as intended application.
Re:Choosing tools for Game Boy development
by svendahlstrand on Sunday January 30, 2022 @04:48AM
(#30135424)
Yes, I've dabbled around with the NES as well. But the Game Boy is close to my heart as I had one as a kid. So most of my projects [3] revolve around that old gray brick.
Edit: It appears to be Z80. Have you done any NES ASM?