I wouldn't call the IX/IY instructions an improvement. They were so slow that they've rarely been used in performance-sensitive code (like games), it totally ma

I wouldn't call the IX/IY instructions an improvement. They were so slow that they've rarely been used in performance-sensitive code (like games), it totally makes sense to drop them in a gaming device. Same for the block instructions in the ED instruction range, quite convenient, but also very slow. LDI/LDD might have been useful for blitting bytes in unrolled loops, but since (AFAIK) the GB video hardware renders tiles and sprites directly, there's hardly a need for copying lots of bytes around. The shadow register set wasn't all that useful either except for quickly saving state in interrupt handlers, but the additional registers take up a lot of die space. On the other hand, the entire block of 256 bit twiddling instructions were obviously deemed important enough to keep them in the Gameboy CPU.