I read this to preread for my 6th-grade daughter who loves romances and fantasy. First off, I have to say that I thoroughly enjoyed the book. I didn't find it slow at all--I read it compulsively for 2 days because I had to know what would happen next and I was picking it up every time I could. If the next book were available now I would immediately buy it and read it to know what happens next. No, it wasn't deep, but I enjoyed getting to know Eureka and her world, and it was a lot of fun to read. For older teen & adult fantasy fans, I'd recommend it in a heartbeat. I just thought it was a fun, quick read.
If anyone else is interested in getting this book for a young teen, I thought I would share some content you might be interested in knowing about (no specific spoilers). There is some gory and disturbing violence, including two gruesome murders. There is a likable character who seems very promiscuous and is described as wearing very provocative clothing and as always thinking about and looking for sex. Teenage drinking occurs at several instances, including as a party-game that is described as a highlight of senior year. The drinking is referred to several times in a positive way; it's something fun they snuck off to do and there were no particularly bad consequences. There is some intense kissing and touching of bodily areas like the scalp, back, arms, and it's pretty clear hormones are engaged and the characters want more. The book goes no further than first base. I didn't note any instances of vulgar language.
If you're looking at this one for your younger teen or tween, hopefully this helps you determine whether it would be appropriate in your situation. If you think maybe not, you might consider remembering the title for a later time--it's a good one!