Well I prefer the Manga to the TV Series as it was the first manga I ever read, but to answer your question, yes! It's fantastic!
I'm a huge fan of the Classic Vampire and Hellsing has put a neat twist on it. The Character design is great for it's genre and having a raving Scotsman as Alucard's Nemisis makes me feel proud!
I just can't (but have to
) wait until Hellsing Ultimate gets a UK release.
As for Immortality discussion, The Manga put's this into perspective and explains almost all you'd need to know
