I certainly wouldn't call it underrated, and it's not exactly obscure these days, but if you haven't played them,
The Legend of Heroes: Trails in the Sky trilogy, as well as the
Trails from Zero/
Trails to Azure duology, are extremely top-tier shit. these are turn-based JRPGs originally made for the PSP in the early 2000s, which weren't released to the US until the last decade. they are very meaty old school type JRPGs, the kind that expects you to be smart about grinding and farming when you need to, optimizing your character stats, and using all the strategic tools given to you in combat. all five games represent probably over 250 hours of play time, and very little of it is filler or time wasting. you can safely ignore the rest of the franchise outside of these five games, especially the recently-released remake of the first game. the dialogue and voice acting will make you want to fucking kill yourself.
by the same developer,
Ys: The Oath in Felghana and
Ys Origin are action RPGs with a heavy emphasis on the action. these are made in the same engine as the Trails in the Sky games but play very differently. they're very fast-paced and have absolutely brutal boss fights. in contrast to the Legend of Heroes games, the other Ys games are actually quite good for the most part.
Ys: Memories of Celceta,
Ys SEVEN, and
Ys VIII are all great games. unfortunately, the developer (Nihon Falcom) has been getting pretty popular, so their newer games are much more expensive and do that annoying shit where there are 500 DLC packs for costumes and consumables and shit, so be aware of that when you start looking at the recent releases.
also by the same developer,
Xanadu Next. this one is more like a Diablo/Zelda clone, almost a proto-Souls game. drops you in the world and then lets you explore and figure shit out on your own. combat is very deliberate rather than button-mashy. this is actually one of the vanishingly few Japanese games that was originally published on PC, so it's actually designed to be played with mouse and keyboard rather than gamepad. there's a sort-of kind-of not-really spiritual sequel called
Tokyo Xanadu eX+ that shares basically nothing with the first game except the name. I haven't played that one so I can't comment on it.
all of these games are still on sale for the next two hours, so if you're quick you can a whole lot of game for very little money.