Random thoughts in no particular order:
Circle of the Moon was actually not made by IGA. It was developed simultaneously by Konami Computer Entertainment Kobe while IGA worked on Harmony of Dissonance in Tokyo. However, to me Circle ironically feels closer to an IGAvania of the two while Harmony feels like IGA was trying to make something partway between Symphony and a classicvania.
Aria and Dawn are generally the best liked portable games, but OoE has a loyal following due to its much higher difficulty more reminiscent of the classic games.
Harmony of Despair is surprisingly enjoyable. Even if you missed the boat, it can still be enjoyed on a PS3 emulator with all the DLC and even online multiplayer. It's honestly a blast.
There's also a mobile game called Grimoire of Souls and, for the really obscure stuff, some Japan only Castlevania casino games.
Of the PS2 games, I remember quite enjoying Lament of Innocence and keep meaning to give it another play someday. The other one I forgot completely.
I'm looking forward to Bloodstained 2!
I'm not normally one to point out a spelling mistake, but there is a very important difference between someone with deficits in lots of areas and someone who defecates in lots of areas.