I confess, I don't actually own a dead-tree copy of Frankenstein. I own about 7 different ebook versions from different publishers, but I don't have a version to consult on, say, a random Friday night when I decide to read Grimly's graphic novel version.
So I can't comment on the fidelity to the text, though the adaptation seemed to consist predominantly of excerpting rather than rewriting. The biggest change--and the best, in my humble opinion--was that Grimly told the creature's story almost solely through the visual language of comics rather than the more text-heavy Frankensteinian narrative. Frankenstein itself is a nested text--we're reading Robert Walton's letters to his sister in which Walton writes the story narrated to him by Victor Frankenstein who, in turn, is told his creation's story. But with each nest, the visual component is further foregrounded.
Obviously, this is not a review of Mary Shelley's Frankenstein. Never let a grad student write a short book review for one of her dissertation texts. It's an assessment of Grimly's success in illustrating the story/adapting it into a graphic novel. On a formal, critical level, I thought he made some brilliant choices--the aforementioned visual/nested narrative link, e.g. or how, as the creature learns to speak, dialogue bubbles become more intelligible. On an aesthetic level, the artistic style drove me crazy. I don't know quite what about Grimly's....let's call it "whimsically hideous" approach was ineffective, but there was a grotesqueness to the characters that seemed odd. First of all, when everyone looks absurd, the creature is not disnguishably awful and that threw me off. And, honestly, I tend to fall on the gothic side of the gothic/horror and I like my villains to look fairer and feel fouler, to paraphrase a certain hobbit
The work itself was quite good, but it was definitely not for me.