I'd like to address the music first. The opening theme suits the tone of the overall anime very well - it's certainly not your typical J-rock/pop opening. This definitely works in Hellsing's favour; after all, if you take away Hellsing's atmospheric, dark feel, then you're left with something that is simply bland and not very well made. The music throughout the anime works well with whatever's happening on screen at the time, but is entirely unmemorable afterwards (I'm normally pretty good at remembering and identifying music from a series years after I've seen it, but today, only a day after finishing Hellsing, I had to hunt down the anime to listen again to remind myself). This is not necessarily a bad thing; it's just not a good thing. Finally, the ending theme. It's a surprisingly happy, hopeful theme that's sung in English. It shouldn't work, to be honest, because it has little to do with the anime as a whole and doesn't contribute to the atmosphere. Despite this, something about it provides a nice counterpoint and I found myself enjoying the ending song quite a lot after every episode.
The characters of Hellsing are varied and each is interesting in their own way. The arguably 'main' character is Seras Victoria, a police officer who ended up biting off more than she could chew when her squadron went to investigate a homicidal priest who turned out to be a Vampire. Along comes Alucard, the other arguably 'main' character, who ends up shooting her through the (amusingly improbable) chest and then giving the dying Seras the dubious gift of immortality. Cue kind-hearted, moral Victoria's angst and growth as an Undead. Despite what you might think, Victoria actually manages to be angsty without being too woeful, and when she finally gives in to the call of her bloodlust it's suitably believable, if inevitable. She's a relatively well-rounded character, if not too special, and I can't think of any particular instance where I found her to be annoying (a rare thing for me regarding female leads). The best female character, however, is most certainly the head of the Hellsing Organisation; Integra Wingates Hellsing. She is calm, proud and dignified without falling into the common cliche of being unnecessarily standoffish, and I have to tip my hat to the creator for that. The backstory for her that was explored in the anime gave her an extra depth and made her seem somehow more relatable than Victoria, depite Integra having lived a much less relatable life. This is probably aided by the absence of ridiculous breastage, to be honest. When she's suffering, you can really feel her suffering, whether it's overt or subtle. Finally, Alucard - he's been talked about to death (no pun intended) by the rest of the internet, I'm sure, so I'll just say that he's one of the best examples out there that anti-heroes do work.
Plot-wise, I think I have to say that the whole thing could have taken half a leaf from popular shounen manga and made the Big Bad Bosses... well, Big and Bad. There was a lot of build-up to the last major enemy of the series in particular, but the fight itself was unsatisfyingly brief and easy when you consider that it essentially became a demon god in an already-superpowered Vampire's body. I think that this may have a lot to do with the fact that throughout the whole series, you're never given any proper indication of vulnerability from Alucard. He's all uber!bad-ass all the time, so when it comes to the point where you're obviously meant to think that he might have been defeated, it all feels a little stagnant. It's a shame, because Alucard could have been a lot cooler if they'd made him just a little less Cool.
Overall, the series has a great atmosphere but a frustrating lack of tension, the characters work well in and of themselves but are too separate to give any feeling of real character-interaction-interest (the only exception is the very last scene of the series between Integra and Alucard), and I quite enjoyed it while it lasted. I can't rate anything except the characters higher than a 7 and rewatch value is basically zero, but I'd honestly recommend the series to anyone who feels like Twilight is destroying everything that good old-fashioned evil Vampires stand for.
