Well, it was mainly code bloat issues caused by the nature of the indexed addressing reach and the need for zero-page indirection. The 6502 instuction set is v

Well, it was mainly code bloat issues caused by the nature of the indexed addressing reach and the need for zero-page indirection. The 6502 instuction set is very simple, and the register complement limited. I don't mean that as criticism, but as an acknowledgment of how the designers made tradeoffs within the die area budget. A good comparison is the Motorola 6800 which had about the same transistor budget but a much more regular architecture. If you study either of those, then afterwards an ATMega168 is going to look resource rich in comparison.