^The tone and story of Persona 2 is not why it failed, in fact the story is widely praised as being the best in the series. What made it fail was that 1, it was a port of a super old game. 2, unlike P1P, Atlus could not market to the P3/4 crowd any longer, since they learned from P1P. 3, the gameplay of Persona 2, while something I can like, I can call it semi poor. Finally, the port was unbalanced and too easy, with frequent encounters. I think they could pull a mature, well told P5 if it has great gameplay and stuff to back it up.
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Persona 2 starts out like Persona 4, tonally, well, not really. Starts out dark, quickly switches to a lighter tone, and zigzags until a certain event where it stays dark. The two tones are represented by the new opening music:
http://www.youtube.com/watch?v=D07mro7NOkA
and the title screen music:
http://www.youtube.com/watch?v=D66Ag8HF_Nw