I was one of the most vocal MegaTentists back when I first started posting on RPGFan. I used to be freaking obsessed with the series and had collected a lot of MegaTen games... which I later sold off to buy a bass amp.
Revelations: Persona for Playstation was my initiation. I actually disliked the game at first and was almost ready to trade it in for another game (I think it was Star Ocean 2) but circumstances didn't get me to the game shop so I decided to give Persona some more time... and I loved it.
At some point, I owned the following and a few I still own:
Kyuyaku Megami Tensei, Shin Megami Tensei, Shin Megami Tensei II, Shin Megami Tensei If..., Persona (US), Persona (import), Persona 2: Innocent Sin, Persona 2: Eternal Punishment (domestic and import), Persona 3 (domestic), Persona 4 (domestic) DemiKids Light, DemiKids Dark, the PS1 port of Devil Children Red Book and Black Book, Devil Summoner (for Saturn), Devil Summoner 2: Soul Hackers, Maken X (if it counts; first Dreamcast game I bought), Shin Megami Tensei: Nocturne (domestic), Digital Devil Saga 1-2 (domestic), the Persona World Guidance artbook, a Persona 1 drama CD (where the main is named Yuuya Narumi as opposed to his manga/canon name of Naoya Toumou), Devil Summoner: Raidou Kuzunoha vs. the Soulless Army, Revelations: Demon Slayer (aka Last Bible)
MegaTen is an insanely prolific series. I never got to try the Majin Tensei SRPGs. I heard Rhonde was absolute garbage and considered the worst MegaTen game ever. I was disappointed by DemiKids especially since its prequels (Red and Black book) were actually very good despite it being kiddie MegaTen. Demon Slayer was pretty dull, but I've heard the other Last Bible games were good.
I used to be a mod on a really good MegaTen forum, so I was surrounded by experts. I left when everyone there started acting like elitist douchebags.
MegaTen is still my favorite RPG series, but I'm not a fanboy any more. I will say that the heavy use of Hindu mythology in the game actually improved communication between me and my parents. I was a self-hating Indian as a kid and seeing Hindu stuff in a cool format made me want to ask questions about Hindu mythology and philosophy.
9/11/1987 was a great day. Namco released Megami Tensei for the NES, based on the novel Digital Devil Story. They released Megami Tensei II. But years later, Atlus bought the rights to the series in 1990 (I think), released Shin Megami Tensei on the Super Famicom and the rest is history. I'm afraid to think what would happen to the series had Namco kept it and not sold it to Atlus.