First and foremost, I write from the perspective of a dissatisfied audience of Vampire Knight Guilty. It was due to my positive opinion of Vampire Knight that led to me to Vampire Knight Guilty and hence my judgement cannot make dichotomies of the two (so I hope you don't mind me making reference to Vampire Knight).
As you'll probably know, VKG continues right where VK left off, retaining much of VK's good qualities at first. The characters from VK/VKG are very well-built and generally three-dimensional enough for me as an audience to relate to and hence enjoy, with the exception of Kaname-kun, who was so perfect in his prestige, power and popularity that there was no room for him to be anything but an admirable and incomprehensible figure.
The artwork itself was generally quite well-done, although I felt the quality didn't follow through towards the end of VKG. In terms of sound, nothing stood out as being special but nevertheless, it complimented the plot and character developments.
The one thing that I really want to talk about is the storyline. The reason why VK was excellent in my opinion was its plot. The flow of the story introduces audience to a very different and intriguing world of vampires, and as you journey through the plot progression, mysteries of the world and its creatures unravels itself through introduction of new characters, philosophies and events, that spices up and quenches curiosity of the world whilst requiting the audience a greater interest in knowledge of vampires and their existence.
And so VKG begins with this highly anticipated and built-up plot where most branches of side and main plots from VK was left wide open. However, as the story progresses in VKG, the pace of the story really dies down. Excluding a few snippets of fair back stories to some of the supporting characters, the main plot really felt mundane and hard to trudge through.
Due to an overly pretentious overemphasis on subtle foreshadowing, the climax of VKG comes about in a very poor, but surprising way, which in its own was interesting. VKG was on a road to revival, bringing back the essences that made its preceder a success. Inevitably, due to lack of pacing in the story, VKG ran out of time to wrap up properly, failing to arrive at the respectable conclusion that VKG's climax opened up for. In all honesty, the conclusion simply felt rushed, as if the writers just ran out of time and whipped up a mediocre ending and forgot about all these other things.
Having enjoyed VK, it really was a pity that VKG did not follow through. VK felt like it created so much potential for VKG, who grabbed a single point of interest and neglected the rest of VK's successful elements. To sum VKG up, it centralises on one element of a good script, then patched a drawn-out and repetitive build up to its front and a short and undermined continuity to its back.
It was not bad, but the fact that it was a mere shadow of its former annoys me, and so I give it a 6/10 (it's simply my opinion).
Nevertheless, if you have seen VK, watch VKG with an open mind. (I don't take into account that I wasn't in it for a fanciful, mystical tale about pretty boys, which was part of what VK/VKG was marketed to be.)