Personally, everything that has to do with Alucard and this universe will always catch my attention. Despite the years the animation seemed very top notch to me, these days I sometimes miss seeing more of this stuff. Very good anime.
As I said, I can't say anything bad about the animation. I think it is pretty decent for the year it was made. My critic is about the story. I felt it a little bit weak in its plot and they missed the opportunity to do something great with Seras.
I'm gonna watch Hellsing Ultimate soon to compare and maybe I'll make a review about it.
Also, I really liked Alucard. He was the best of this anime.