" I can’t tell the leaf fall was because of the drought this summer or because I put it in full sun. "

Very likely a combination of both, especially with a newly planted, not yet established tree. And the vast majority of cultivars would prefer some shade or relief from intense afternoon sun anyway, let alone be drought stressed. Doesn't look that bad, considering :-)

If you are referring to the cultivar Mikawa Yatsubusa, that is a selection that will tolerate full sun well provided all watering needs are met. Mine, being grown in a container, is being moved to a sunnier position next season. It is now in all day dappled shade and just does not develop good fall color in that position.

And keep control of that ivy growing at the base!

full sun in NJ is not all that intense compared to about 80% of the rest of the country... eh ...

IMO ... ALL LEAF DAMAGE THIS SEASON was stress related.. moving it from grower.. to seller.. to your house.. then you planting it.. and how you cared for it after.. plus all weather related stresses ... to suggest the sun variable was the only or most important variable is a step too far ..

water deeply into fall.. meaning.. give it one more deep drink.. let the hose trickle for a few hours while moving it around ...

and finally.. its NOVEMBER.. we dont really care about how ugly the leaves are.. nor what caused it... they are SUPPOSED TO FALL OFF.. and they usually get real ugly before they do..

so all you are left with.. is a good deep drink...

ken

ps: the above goes for all trees... what tree you are dealing with doesnt really make a difference ... its stressed ..

Here few Acer palmatums handle full sun. Before you give up though give it another year. My thinking is the first year in the ground is difficult for anything. Yours held leaves until November which I think is reasonable flr your area.