IT SHOULD FIRST BE SAID THAT I HAVE READ THE MANGA AND THEREFORE MY ARGUMENT IS BASED ON THE DIFFERENCES.
This anime greatly disappointed me because it removed the comedy and high quality action of the manga and OVA. What it left behind was merely a husk of what it could have been. Many of the characters lacked the depth that is seen in the manga. Alucard is not the sympathetic character that secretly wishes for death. Walter's story lacks the betrayal. And the Nazi villains that plot to engulf the world in war are completely absent. Instead, the anime provides the Gary Stu villain Incognito who is defeated against what appear to be all odds.
My primary complaint is not that the anime diverges from the manga, but that it does such a poor job.