This game really likes to toy with your heartstrings, and does so very well. The reused Jenny loss motif was done just enough to not get annoying, and the mental illness plot twist really added a lot of dimension to the story. The actually chose the "Stay with Jenny" ending first, and was by far an artistic, beautifully done ending which, if it were the "true ending" of the game, would've placed it on that "games can be art, yo" mantle that so many people like to use to show off the medium. The "stay with Jenny" ending forces you to come to one of two conclusions:
a) Jackies mob life and Darkness powers are just delusions, and he loves a woman he can never really have.
b) Jackie's inability to let Jenny go has forced himself to surrender to the Darkness' tricks, accepting defeat and living in a fantasy world as he is being rebuilt to be an empty shell for the evil power.
Both options are absolutely fantastic and really grow (or in the later case, complete) the characters growth. The slowdance at the end with Nurse Jenny/Fake Jenny is also oddly much more heartfelt than the true ending. I actually found myself choking up a bit as it faded to credits.
It's a shame then, that the "true ending" is such a poor one. Ultimately there is no character growth in it, just a shallow cliff hanger to set up another antagonist, to continue Jackie's one note Jenny revenge quest to Darkness III.
I for one will be accepting only the previously discussed ending as the true ending, because in either scenario, it's just fucking poetic.