I think if you're curious to see what Kingdom Hearts looks like now, it's worth a peek at least. If you don't like Kingdom Hearts, or rather "Kingdom Hearts" in the same way people say they love or hate "anime", then don't bother. KH3 is that in excess.
There is some interesting things you might appreciate if you've been a fan of the series up till now, but it mostly asks that you either have a healthy amount of nostalgia for the series or are seriously devoted to the lore (or both, really). It's a bit of a mess, but it's not without charm. It wears a bit thin, and feels half-baked at points, but if you squint and give yourself over to "Kingdom Hearts" instead of Kingdom Hearts you might get something more out of it.