ooh it's hard to pick just one! i had quite a few books i rated 5 stars for various reasons (easy reading, quickly got me hooked, emotional and/or moving, solid ending, likeable characters etc) so these would be my faves for the year:

you'd look better as a ghost by joanna wallace
the midnight library by matt haig
a tale for the time being by ruth ozeki
tokyo ueno station by yu miri
wolfsong by tj klune
chlorine by jade song
even though i knew the end by c.l. polk
payback's a witch by lana harper
brown girls by daphne palasi andreades
silver in the wood by emily tesh
book lovers by emily henry
still writing by dani shapiro