What are dialectical, grammar or morphological, differences between modern Northern Greek and Southern Greek?

This graphic from Varieties of Modern Greek has been used around here before:

The main difference is phonological. It’s one difference, but it’s a doozy (purple line): unstressed /e, o/ are raised to /i, u/, and unstressed /i, u/ are deleted. That makes Northern Greek sound at best silly to Southern Greeks (though their attempts to imitate are as unsuccessful as you’d expect). If you add some more phonological changes on top, you get something like Samothracian Greek, which is not comprehensible at all.

Some morphological differences: Northern Greek avoids the genitive much more, and has some different inflections. Not much in the way of lexical differences.

The Northern/Southern distinction is the oldest distinction made between Greek dialects, introduced by Georgios Hatzidakis in the 18mumbleties. (1880s?)  I hold with Kontosopoulos’ proposal in 1983, that the really important distinction in Greek dialect is Western and Eastern—or to use terms Greeks might be more familiar with, Mainland and Islander.