Like the first book, this one also has a lot of rich world-building history and a well-rounded story that unfolds nicely. Some events feel rehashed, but still ties in with the plot properly. I DO find it rather amusing that it feels like a running gag that Yelena's life is never going to be peaceful or quiet and that she'll always be looking over her shoulder or fighting for her life -- at least THAT makes things interesting.
Again, while the writing is good, I still have some quibbles about the tone and the style -- we range from getting a more historical style of speech to more modern styles, and on top of that, there was some cheesy dialogue inserted at certain points. The plot twists are fairly predictable, so there seemed to be no element of surprise anywhere. Events happen and then events pass and there's really no time to really think about them, so half the time my "Feels" were probably only in the "Ready" position, never making it to the actual "Feels" part. So a lot of the events, to me, were kind of "meh".
Also, there felt to be a lot more telling than showing, but that didn't really bother me much. I mean, this is a first person POV after all...
The characters drive this book more than anything, much like the first book, and without them, the story might still be enjoyable, but it would run a bit flatter and get boring fast.
Yelena's kickass, Valek's awesome, and the rest of the characters form a terrific supporting structure around these two (even though we barely get to see Valek until the last half of the book). Unfortunately, none of the other characters in this book really leave a lasting impression.
Leif made an interesting obstacle, blood-relative or not, I haven't gotten around to forgiving him as easily as Yelena has (which makes her more magnanimous than me) since he generally spent most of his time trying to get his own sister killed. When he first presented himself as the suspicious, arrogant, rude, condescending prick that he is, I already foresaw a couple betrayal actions coming from him
Overall, Magic Study was a good and enjoyable read. I especially appreciate that the references to the first book were strewn throughout the book rather than concentrated as an info dump at the beginning. It always helps the story flow much smoother.