I will always have a deep and abiding love for Sir-Tech's Wizardry games. I appreciated how gritty and unforgiving the gameplay could be, and how rich the (mostly text-based) story was. I started playing Wizardry I and II on NES, and then picked up Wizardry V in college after it was released on SNES.
I never really was into the Wizardry series after the first three (Proving Grounds of the Mad Overlord, Knight of Diamonds, and, um, something with L?). I vaguely remember 4, but by that time, I had moved on to the Bard's Tale and Might and Magic.
My first love was always the Ultima series; I-IV will always be the formative games for me.