Gotta crank the obscure to the max like He Man and the power of Grayskull
Atelier Annie
Started playing this one a few days ago and it's kinda fun. It's also the most forgotten Atelier (that released overseas). It's one of the first localized before we got Ryza, Yumia, and all that. It's the second game in a spinoff trilogy that went mostly unlocalised (Lise, Annie, Stahl). Atelier Lise is well known for being the only actual bad Atelier game that was prone to so many freezes that they made a second version that was fixed with a different color, hence why it wasn't localised. Supposedly, people took to calling it "Atelier Freeze," which if true

. Not sure why they bothered with Annie though if not even Stahl could be localised though. Despite having positive reviews, the opinion on this game is incredibly divided. Most forgot it even existed, a lot more seem to hate it and view it as one of the worst games, and a minority love it. Here's the only video essay on it.
Custom Robo Arena
If I'm taking to talk about any Custom Robo, it's gonna be this. Battle Revolution has the more interesting story but Arena has more content, more robo options and a better artstyle. Seriously BR's graphics are kinda dogshit outside the arena and the characters are especially done dirty. Still recommend playing that game though, especially since it's one of the only to be localized at all.
A Witch's Tale
This is a...very unique playing turn based RPG. Good unique btw, not ominous unique like something along the lines of Gal Gun. If you know of DS Wizard of Oz, it's very similar to that.
Mojib Ribbon
Vib Ribbon's getting a lil too popular now, so here's its sequel. Little known fact is that Vib Ribbon is a trilogy (Vib Ribbon, Vib Ripple, Mojib Ribbon). Ripple is ass, but Mojib Ribbon is the closest to the style of the original. The entire game is spoken in Japanese though and very reaction based. Some beautiful calligraphy too.
Medabots
I like the risk/reward style of gameplay. The battles are dependent on parts and make/break a battle. If you lose every part or someone destroys the head, the winner gets one of the loser's parts. And yes, this also includes you and incudes even the default parts. There's a couple different attacks to use, like using the antenna to raise your accuracy or using one of two arms to go for (often) one of the lower body parts. There's two versions, and everyone agrees Metabee is easier, but I did not know this and started with Rokusho, which is also pretty easy, just slightly harder without range.
Dezaemon Kaite Tsukutte Asoberu
If this made it overseas, its influence would be MASSIVE. Dezaemon predates both Mario Maker and Mario Paint and does the good qualities of both arguably better. This franchise is all about making your own SHMUP, background music, graphics, bullet patterns and all. Devil Engine was actually made on Dezaemon 2 for Saturn. Naturally, it may be a bit of a chore figuring out how to use these games because the documentation is non existent, so experiment. The music maker allows you to do pretty much what Mario Paint does but with more accurate SNES instruments and sounds. It also allows you to change the speed, key, create multiple layers (only 2 in the game I'm specifically mentioning but 2 and Plus have like 5 layers), and make a 16 sheet long song, more in the sequels. If you're a fledgling music maker, then I can't recommend one of these games enough even if you don't want to make the game because it's good experience. There's 5 games in total: Dezaemon (NES), Dezaemon Kaite Tsukutte Asoberu (the one being mentioned) (SNES), Dezaemon 2 (Saturn), Dezaemon 3D (Nintendo 64), Dezaemon Kids (PlayStation 1), and Dezaemon Plus (a remake of Kaite Tsukutte Asoberu) (PlayStation 1). Just don't start with the NES game or 3D, they are far too complicated for how little documentation they have. I have not tried Kids yet.
Guwange
I could put nearly every CAVE game in this list but they all have their own niches minus another I'll add to the list. Guwange doesn't really have this. It's quite the unique shoot em up, it's very slow to simulate walking. Each playable character has a different shinigami next to them and you can move it around. Of course this means the bombs are different, but this also leads to another unique mechanic. If you point the shinigami in a direction, any bullets going that was will actually slow down while in range and you can use this to dodge some pretty good hits. It has eh music, but the gameplay and graphics combined with the strange boss ideas more than make up for it.
Muchi Muchi Pork
This is the other CAVE game without a niche. It's very similar to the Ibara series also made by CAVE as well as Battle Garegga by Raizing but the catch is pigs. Everyone is pigs. Even the playable girls. You like pig girls? Well now you do, I don't make the rules. Also it has this 10/10 intro (holy shit I am the first result when looking for this song)
Rosenkreuzstilette and Rosenkreuzstilette Freudenstachel
One of the earliest non fan game Mega Man likes. They're very derivative of the NES games, sometimes to the point I'm surprised they even sell them on Steam without Capcom knocking down their door, but they're really fun games with a really interesting story. They're a mix of Mega Man gameplay and Castlevania artstyle and you can especially tell in some of the more industrial stages. There's even a Dracula clone in the first game. In a surprising twist, Alpharad actually did a video on the first game a while back, but even that managed to not save these games from obscurity lmao.
eXceed 3rd Jade Penetrate & Jade Penetrate Black Package
Really fun Touhou like shmup (and it's remaster) that got dealt the worst cards imaginable. Publisher went down, developers went down, and the people who grabbed the rights to the franchise did nothing with them. Hell Capcom even published the localisation of these games (store page is actually still up) but they didn't wanna bother it seems. The only claim to fame this game has are but its composer (which is THE S.S.H.) and the final boss theme Intersect Thunderbolt (took off on Osu and is close to reaching 1M views as a result). These games are abandonware, but both are on the archive among other places.
Gravity Circuit
Honestly debated putting it here because of all the video essays that exist for it now, but looking further into it, even those video essays have NOT taken off so. You'll get the most mileage if you enjoyed the Mega Man Zero games. Also one of the few games available on Mac so you can literally play it on anything. Also the music slaps, but that's inevitable when it shares a composer with Mega Man X Corrupted.
Rabi Ribi
Let's end this list off with a bunnygirl. Rabi Ribi is an action Metroidvania with the bullet patterns often found in shmups and bullet hells, with these patterns also being common with the enemies. Sounds like hell, but it's quite nice. It has some incredibly deep combat and a whole lot of options and it's ballbustingly difficult, especially the post game. It has some AMAZING music too, second best of all the options behind Gravity Circuit above.
We'd be here all day (and I'd reach the attachment limit) if I talked about everything so I'm cutting it here.