Byte addresses was the feature I think was the most important, on the 360 and the pdp 11.
The PDP 11 dropped short form addressing, and that gave it the power over other 16 bitters,
insert ad for building a 18 bit pdp/k PDP-K - Computer History Wiki
Almost any other feature off hand could be seen on other machines.
Load effective address, while useful also needs to paired with Add effective address,for machines with out ([base][index]) addressing. This is my hack for a addressing mode.
(A potentially distracting comment relocated from a personal history thread.)
(Everyone: If you have a new idea, please start a new thread - and by all means link back to the current one.)