Impression One: Use of the first person present progressive tense in a novel gets tiresome. While many would argue that sentences like, "I am running down an alley, sobbing," put the reader directly into the action, I would argue that being constantly told that "I am doing this," and "I am doing that," gets distracting - not critically so, but enough that I had to fight the impulse to put the book down in the first couple of chapters.
Impression Two: Libba Bray definitely knew her material. A Great and Terrible Beauty reads like part gothic romance, part Victorian pulp in the tradition of H. Ryder Haggard's She, and Bram Stoker's Lair of the White Worm - there's lots of occult danger and Eastern 'otherness' (both sexy and threatening to a respectable, young Englishwoman), lots of lurid drama. All in all, it's pretty fun.
Impression Three: Libba Bray also really knows young women. Gemma Doyle is a good heroine, as far as teen-age heroines in historical fiction go - she's active, she has agency, she's flawed but passionate. There's a fair amount of conflict and fight in her, which would make her easy for a modern teen to relate to. Gemma's friends are also interesting - the drab, unattractive Ann (who is a cutter, due in large part to her implied depression and alienation), the gorgeous, ornamental Pippa, who just wants to be loved, and Felicity, who, of the four, has the most force of personality and complexity. They're an interesting mix of types and not one that comes together easily (there's a great deal of initial antagonism). Though I found the progression of their friendship to be a little forced, it was also believable in that there are girls for whom dislike is an automatic precursor to respect. The four of them together make a pretty interesting dynamic.
Overall, A Great and Terrible Beauty is quality YA - fun, dark, a little edgy and sexy in a historical way. The thing I liked most about it however, was the fact that all four of the girls, Gemma, Pippa, Ann, and especially Felicity, want autonomy - they want personal power, they want to valued for themselves, they want to be heard and, in their own way, they fight for that privilege in a Victorian world that valued silence in its women and girls. For that alone, A Great and Terrible Beauty is worth reading, though I'm not quite tempted to read on in the trilogy.