The interesting thing is that I wrote very little of the code by hand; instead I wrote a program that generates the opcode implementations from a concise specification. The end result is remarkably compact, and the whole thing was really fun to make.
Did you use this for generating the opcodes? The Z80 ISA encoding is quite regular and octal-based: http://www.z80.info/decoding.htm
As for the improvement, I never liked switch, for unknown reasons :) You mean an improvement in style, performance or both?
IMHO the switch would improve both style and performance, what caught my eye when I looked over the code was that different flags would require different amounts of time to execute, which really seems an odd thing for an emulator to do.