The GBC is a significantly more powerful machine than an NES, with some caveats around graphical rendering. The NES is a MOS 6502, the GBC has a weird chip by

The GBC is a significantly more powerful machine than an NES, with some caveats around graphical rendering. The NES is a MOS 6502, the GBC has a weird chip by Sharp that hybridizes a Zilog Z80 and an Intel 8080 clocked about double in Game Boy mode and quadruple in GBC mode. The GBC also has sixteen times more RAM, eight times more VRAM, supports bigger carts (up to a megabit), and twice the palettized colors on screen, albeit with marginally fewer sprites. Huge difference in hardware--the primary reason the GBC is looked at as being "NES-like" is because of the lateness of its release and the comparative jump to the GBA, which is a recognizably modern ARM environment.