Its an excellent show, one of my favorites. It is a rather serious story, but fortunately there's enough humor to keep it from being unrelentingly dark.
The action is great and often much better than what goes on in the standard fighting anime. The characters are mostly interesting, and the superb score helps make a scene appropriately creepy or sad or epic when necessary. I actually own the soundtrack Geneon released, that's how much I liked it. The mythology is awesome too, with the servants coming from different parts of legend.
I got my hanRAB on the entire release, but I do hope it's salvaged eventually. I have no illusions about the fact that any series coming from a visual novel is rather niche, but the quality is so high its in its own class. And most shows like that are all about moe or boring, rehashed harems or love triangles, whereas the Fate/Stay Night series is every bit a fantasy adventure.