With all the fantastic teachers in Columbia's Slavic Languages department, it's difficult to imagine why anyone would want to endure the abuse and aggravation of a semester with Sergey Levchin. Having immigrated to the States sometime during high school, he speaks both English and Russian perfectly and is therefore is able to be really lazy while managing to appear competent. A good foreign language teacher, I've always felt, should work to foster a environment where students feel comfortable using their imagination. During class, not only does Sergey make his students feel as if all their sentences are boring and stupid, but God forbid you should make a mistake of case by saying x instead of y. He'll cut you off mid-discourse with a scornful "Pochemu x?!" rather than tactfully slipping in the correction sidewise.
To his credit, his assignments tend to be very useful and entertaining, such as having us translate short poems from English to Russian while preserving the rhyme scheme. He'll also occasionally try to get an informal linguistics debate going, which could have been interesting, if it weren't for the fact that he would rather dismiss a student on the grounds of some semantic quibble than hear anyone criticize his own pre-established opinions--talk about insecurity!
In conclusion, if getting a good grade and practicing your grammar is all you care about, then I suppose there's nothing wrong with taking Sergey's class. But if you're taking Russian for Russian's sake, and are looking for a good classroom experience, then by all means steer clear.