It really depends, there's a few types of Jap games, and they really don't deviate that far from these categories.
The newest pet project of the jap, everyone wants to be some sort of weird mix of Skyrim, GTA and your traditional JRPG, with some other misc shit the directer played on the only Xbox 360 in japan. Obvious examples are MGSV, BOTW, FFXV, Nier:A, and DD. Some of these are not awful, they realized some of the good things the aformentioned western games did and cut the fat. Most of the time though? It's a boring slog of a JRPG with all the boring slog-like elements of a western Open World games, Playing MGSV and BOTW is like pulling teeth they're so boring. Japs seem to use the Open World as a crutch for shitty level design even more than the western industry does, for the most part these games are awful.
You all know the deal with these, hit or miss to begin with, and hit or miss as to whether or not you'll actually enjoy these games, Stories are usually at least a little bit interesting, but there's a lot of super generic crap in here too.I personally loath these types of games with few exceptions that actually mix up the battles either with timed inputs or the Rhythm game built into Mother 3's battle system. Not the worst genre, If it ain't broke, don't fix it I guess, but not my thing.
A lot of overlap with the first and second category here, but same general concept, real time combat, usually hack and slash, with JRPG plot, usually not too deep, but on the rare occasion it is it's a nice combination
Sort of obvious, but should probably be stated, Nintendo isn't the only one, there are some jap indie platformers that are pretty good, La Mulana, Cave Story, Momadora, etc, don't see too many of these
Senran Kagura, Valkyrie Drive, Gal Gun, DOAX. These games are for you to cum too, no one does, nor should play these games without some lube near-by, and there's nothing wrong with that, but their enjoyment is 75% titillation, 20% masturbation, and 5% actually enjoyable gameplay, I should know, I grinded in SK2 just so I could play dress up with the girls in the gallery to jack off to later, Ditto for DOAX3. When people think "weird japanese games" this is what they're really talking about, these are the "games" japan makes that as games I can't stand, but as fap material I enjoy thoroughly
When people say they hate jap games, it's usually the borderline porn games that they're talking about and conflating with the actually good shit.