TLDR: Probably the worst kingdom hearts out of all 3 (in comparison), still a good game.

Been wanting to buy the entire kh trilogy on steam for a long time, ended up doing it on summer sales, it was like 40-50€ for the complete collection which is nuts (and it was the ONLY game I bought on summer sales which is crazy).
Played the original and 1.5 2.5 on consoles so got some knowledge of the series, but had 0 knowledge of kh3.

In comparison, kh3 literally has everything the other kingdom heart games have, barely anything new.

My initial purpose was to get 100% achievements but started a normal difficulty save and figured out 60 hours in that I would have to throw that one into the bin due to exponential danger.

The biggest threat in terms of achievements for kh3 are the data battles. Late game 1v1 battles against overpowered enemies (organization XIII based) which puts your skills to tests.

KH2 data battles were fun, fair, enjoyable.

KH3 data battles are like x4 times harder than kh2 by default, and they "FORCED" the achievements community to use "PRO" codes (that enchance gameplay difficulty by another x10 by adding triggers like HP, MP drain, no ultimate combos.. no magic… 0 DEFENSE….) in order to get those achievements.

Also the game has 350 collectibles that u must get for the achievements (chests and stuff).
I spent like 4 days only for the data battles on BEGINNER MODE and lvl 99.

I also did 100%d kh1.5 but that's another future story.
I'm a little bit burn from kh rn so I dunno if i want to do another kh 100% yet.