Let's see if I can hit all the clichés without spoiling too much of the plot. I think the moment it started for me was when Jemma, the new-girl-at-the-high-school protagonist, dropped her books and the dreamy love interest picked them up for her. It continued through the bad boy one immediately pegs as a vampire turns out to be, yep, a vampire. But that one's a little forgivable because this is YA (younger readers may not have read as many vamp books as adults) and there's a spell on the protagonist that prevents her from cluing in to vampiric presences. The moment where it stopped being fun for me was when the protagonist turned out to be a vampire Slayer… yes, of all the terms in the world, that's the one the author chose.
There's a world-building info dump about Nephilim and supernatural bloodlines, which might have scored some points if it weren't followed by a barrage of labels like Shifters and Keepers and Casters, all coming at me until I totally did not care. Almost every named character in the elite high school is a supernatural woogums of some sort or another, and somehow they can keep their mouths shut about it unlike every high school student I've ever met.
This is too bad, because the characters have some decent interplay amongst the stereotypes; rather than just being standard shallow teens, they're motivated as often as not by convincing reasons like "If I don't lie about this important thing, it may lead to my death or hers." This lends the story a little weight and some nice characterization. There's also some genuine angst as Jemma's backstory gets explored through magical means.
But that doesn't matter as much as you might think, because like so many urban fantasy series these days, Inception is just the first volume and doesn't have a proper ending or climax. It's a cliffhanger, and so can't be judged on the merits of its incomplete story. Plot threads that might have come together to give the protagonist more trouble (like the jealous mean girl who exemplifies the non-supernatural life Jemma can't get together) just kind of fizzle with a promise that the next book will answer all my questions. I remain unconvinced. I'm rating this 2.5 out of 5, with the 0.5 extra for the layered characterization. I'd be on the fence about recommending it to a YA audience. I liked it better than Twilight but considerably less than strong YA bestsellers like Hunger Games or HP. It did manage to soak up a lot of time on my flight to Beijing, though, so at least it's got that going for it.