[quote name='FlamedLiquid']May be a dumb question but how different is Hellsing Ultimate compared to the original series?[/QUOTE]
Hellsing Ultimate follows the manga, while the original series followed the manga up to episode 5 or so before making shit up. Ultimate has fantastic animation, but the ending stumbles and falls apart since the manga ending also falls apart and makes no sense. So if you're a fan it's worth a shot, just be prepared to come out angry and confused over Alucard and many other things.