This forgotten classic of the series was released at the very tail end of the PS1's life cycle as the PS2 was coming to dominance, so Eternal Punishment didn't make as big an impact as it could have were it released earlier in prime PS1 RPG time.
Eternal Punishment was still figuring out its various systems and hadn't perfected them yet, but was a big jump up from the original game. Its also interesting to note that it wasn't actually the second Persona game -- it was the third.
Previous game Innocent Sin didn't make it to the U.S. on the PS1 at all and in fact didn't arrive for North American audiences until 2011 on the PSP. Obviously, the story of Eternal Punishment could be confusing at times, since none of us had ever played its predecessor.
While it may have been a bit baffling at points, it was also incredibly dark (like Rule Of Rose dark) and will always remain with those who played through as kids and had no idea what they were in for. Horror fans will particularly note elements taken from the Cthulhu mythos, like a character named Nyarlathotep.