This series is barely known but it is one of my favorites. I even have the second game in the series which even fewer people knew came out. However if that is too mainstream for you I can go even further:
It was one of the first games on the PS2 and I barely know anyone who bought it. I had gotten it when I got my PS2, its based of an anime Sorcerous Stabber Orphen and its not so bad. I can barely understand how it even made it to America. If I am challenged I can go further.
Jagged Alliance 2 and X-Com: UFO Defense. While the latter is more well known, both represent the pinnacle of tactical combat mixed with some sweet RPG elements.
Jesus Christ yes for the X-Com. It was popular in its day, but when I'm asked what my very favorite video game is, and I reply X-Com, or I mention it in any other context, I have never once had someone know what the hell I was talking about. After talking about it and naming it as my single favorite video game ever for several years, I finally got one of my friends to try it, and he absolutely fell in love with it. Which pleased me greatly, since I thought perhaps much would be lost with age.