The story was compelling, and I read through the last 20% or so really quickly as I wanted to know how it ended. So in that way it had me hooked.
What bothered me though, and what really makes the whole story kind of "meh" is that the main character behaves incredibly stupidly. I'm all for flawed characters, but there's a difference between flawed and "makes the idiotic choice at every turn and never learns from their mistakes". Jake sadly falls into the latter category. And for a psychology student (actually any slightly intuitive person) it took him way too long to figure out his motivations for helping Anna. Again there's a balance between making the reader seem smart and making your characters seem dumb.
The budding romance also added nothing to the story as there wasn't really any build-up to make you care about or believe in it.
The writing was pretty good, it was a quick and easy read, and it was nice to virtually walk the streets of Vienna, but overall my annoyance with the main character lands this novel no higher than a 3.