Flags can differ too: the DAA instruction clears HF in the GBZ80, but not in the Z80.
An oddity is that ADD SP,e takes 4 cycles, while LDHL SP,e takes only 3 cycles.
Fun fact: Way more GBZ80 cores were produced for Gameboy hardware (118 million Gameboys and 81 million GBA) than all the Z80 chips produced for home computers and game consoles. [https://www.chibiakumas.com/z80/Gameboy.php Learn GBZ80 Assembly Programming with ChibiAkumas]