Atlus is pretty notorious for shipping small amounts of games to retail, anyone who follows them knows that if they release a game you want, you better get ready to pay full price cause finding a copy later can be a problem if the game is super popular. Finding the original P3 or it's Director's Cut FES can be an issue, course the Persona games are not as difficult to track as say... Digital Devil Saga, SMTIII:Nocturne, or the first Disgaea game on PS2.

P1, is decidedly old school, and I can only recommend it to completionist or people who really enjoy old school dungeon crawlers. P2 (both games, don't ask... ) is considerably better but probably still too "old school" for modern RPG tastes. P3 is the newb friendly entry and introduced the popular Social Link system that newbie fans adore and old school fans hate. It's often considered to be the FFVII of the Persona franchise cause it actually became a cult smash hit that made the series popular, and is still one of the best selling entries in the series receiving an awesome Director's Cut, an anime sequel, and a revamped port to PSP. P4 is also just as popular and is getting it's own revamped port for Vita and has spawned an anime series, and a musical in Japan.

I heard part of the reason that P5 is taking so long is because the team really wanted to revamp elements in the game like P3 did for the series, and after playing through Catherine, I'm interested to see what they have come up with.