-Homura: Easily Taito's most obscure shoot em up without even a (proper) wikipedia page or much info at all. It's an arcade game ported to PS2, and both stayed in Japan
-Thunder Force VI: the only Thunder Force to stay in Japan and also the only Thunder Force to be MID AS ALL HELL. It rehashes a lot of older idea from the previous games to the point there's absolutely nothing really original about it. It especially takes from the predecessor and it shows. Saddest part is that not only was this the last Thunder Force game but the original Thunder Force VI was gonna be way different before the project was cancelled due to Technosoft being bought out by a pachinko company + shutting down due to a merger, EA style
-Odin Sphere: Definitely
less underrated now, but be honest how many people know about it? Really beautiful action RPG with a lot of deep combat and crazy combos. People often pass it up for Leifthrasir being the more up to date version, same with Persona 4 Golden to Persona 4.
Odin Sphere (PS2 gameplay)
-Metal Slug (3D): A 3D reboot of Metal Slug that...is quite the game. I recommend playing this only as a novelty, especially after playing all the mainline games first. Matter of fact, go emulate all the Metal Slugs, they're all on PSP (XX is a substitute for 7). You could buy off Steam too but it only has 1-3. And iirc, I think GOG has 4. 5 and 6 are MIA. If there's one good thing to come out of this game's existence, it's this badass GaMetal cover
Out of Control (GaMetal remix)
-Raidou Kuzanoha duology: I know HD exists now but it's already gonna be a glowup from Soulless Army. I hear RK2 is great though.
-Nocturne Maniax Edition: There's a few minor details that HD added or subtracted. I hear HD messed with an ending too. Also this version of Nocturne has a free Dante with it NOT locked behind $15 so yeah
-GrimGrimoire: This is the Vanillaware game even I sometimes forget exists as well. It's a pseudo point and click game which in the PS2 era is very eye catching. The art is gorgeous too (as usual), so play it
-Castlevania: Curse of Darkness/Lament of Innocence: I hear both are really good for 3D Castlevanias, but haven't played them for myself
-Dodonpachi DaiOuJou: This is kinda the best way to play it besides Reincarnation, so good that developers at 5pb tried to plagiarise the code for the Xbox 360 port (and failed)
-Ibara: Arcade port with added music
-Every Atelier game on PS2: They're all pretty good, especially Mana Khemia. There's also a fan translation of the PS2 port of the first two Atelier games ever, if you wanna try those.
-Zone of the Enders 1 & 2
-Ridge Racer V
-Gradius V
-Radirgy Precious
-Twinkle Star Sprites: La Petite Princese
-Shikigami no Shiro II
-Rez
-Xenosaga Episode I-III
-Espgaluda
-R Racing Evolution
-The Red Star: SHMUP based on a graphic novel
-Radiata Stories
-Ar Tonelico I & II
-Virtual On Marz: the last Virtual On game and a pretty fun one
-Suikoden III-V
-Baroque
-Raiden III
-all Psyvariar games
-Haunting Ground
-Gauntlet Dark Legacy
-Dawn of Mana
-Phantasy Star Universe
-Scarface
-Dead or Alive 2
-R Type Final
-Shadow Hearts trilogy
-Fatal Frame I-III
-Kuon
-The Rumble Fish
-Gunbird Special Edition
-Metal Saga
-Dark Cloud 1 & 2
-Gungrave
-Clock Tower 3
-Puyo Puyo Fever 1 & 2
-Rule of Rose
-The Suffering
-Bloody Roar 3 & 4
-Evergrace 1 & 2