Shin Megami Tensei is an amazing series. They can be pretty challenging, but it's so, so satisfying. The Persona series is the most popular subset, but you're likely to get a LOT of replies talking about them (for good reason) so I'll stick to the main series.
In each game, you play as a human (or ex-human) in a world filled with demons. For the most part, this character is your only consistent party member. You recruit other members from the ranks of the demons by conversing with them during the battles instead of fighting them. Demons can be fused together to create new, more powerful demons. There's a bit of elemental rock-paper-scissors with the combat, to the point where some of the games afford you an extra turn for exploiting enemy weaknesses. They also get this privelige, though so be careful.
The games are no slouch, narratively either. IIRC, the first two games tie in together but, while it is canon, the third one (Lucifer's Call in EU, Nocturne elsewhere) is it's own thing. Strange Journey is technically a spin-off, being narratively unrelated to the others, but it plays like the other main series games and is my personal favourite. Each game is quite dark in it's way and relatively none-linear. There are normally at least three different routes you can take through the game, based on your alignment. The three alignments are Law, Chaos and Neutral. Don't mistake this for Good, Evil and Neutral, though.