As someone familiar with z80, 6502, and 68HC11 instruction sets this breaks down the key differences between the "6s" and "8s" archs well. I personally learned z80 first, then found the 6502 a bit limiting after writing z80 for a bit. That said, I still love writing bare metal 6502 for my Atari 2600's handicapped 6507 (missing an address line among a few other oddities). Sometimes limits are a good thing. I certainly would never want to remember all the more complex cisc instruction sets for example.