@Phantom_Trickster
Let a mainline SMT elitist step in here
P3 is about as dark as P5 in terms of tone, I'd say the gameplay is worse though. If you're gonna play it, I would recommend the PSP port, Persona 3 Portable. In PS2 versions of P3, you can't control your party members, but they changed that in P3P.
P2 (Both Innocent Sin and Eternal Punishment) have pretty old-school gameplay, and the battle system hasn't aged particularly well. It takes some getting used to, but it's still a good time. The story in both games is phenomenal, more than reason enough to play them.
P1 has also aged roughly, but it's still very solid on it's own. I urge you to give both P1 and 2 a fair shot before ditching them because they are really good.
TL;DR: Start with 3, then 4, then either the older Persona games or you can delve into the weird world of P4 spin-offs.