I can't really say a an anime in particular, but a series is my favorite - Fate /. The series grabbed me early on with Stey Night, which lead me into my love for the source material (it's visual novel). When Zero came out I was absolutely enthralled with the notion of more of my favorite series. I wasn't disappointed in the least.
My second would have to be the Ghost in the Shell S.A.C. Series. While the individual eleven may have been something rather low on the bar of expectations, the laughing man saga was amazing for me from the start to the finish.













