The instruction encoding is quite regular -- it follows the 2-3-3 pattern that came from the 8008 (if not earlier), and thus looks much better in octal than hex:
> The instruction encoding is quite regular -- it follows the 2-3-3 pattern that came from the 8008 (if not earlier)
While it is true (and I am aware of it) that the Z80 instructions follow the 2-3-3 pattern, it is nevertheless not that regular. Best look at the "purest example" for this that is referred in the literature all the time and acted as a model for the criterion that in RISC the instruction format is very regular: the instruction format(s) used by MIPS. Here there only exist 3 different types of instruction (R-type, I-type and J-type) and all have a very regular pattern. One can find very suggestive pictures at
Look at the instruction encoding
The instruction encoding is quite regular -- it follows the 2-3-3 pattern that came from the 8008 (if not earlier), and thus looks much better in octal than hex:
http://www.pastraiser.com/cpu/gameboy/gameboy_opcodes.html
http://www.z80.info/decoding.htm
As for everything else, I would agree with you --- it's not RISC.