Walkow is one of my favorite professors. Most people think he is hard. That's true. His midterms are quite challenging and his final takes the full 3 hours to complete. But on the other hand, he explains concepts very clearly. His lectures are very well structured and his voice is loud and clear, so you can easily follow the lecture without getting asleep. Also, he gives you extra-credit opportunities. And you don't have to buy a textbook, all material are given on slides in clear and understandable manner.
I took Walkow for Linguistics 20 (which is the intro class for Ling majors) and hated him with every fiber of my being--as a teacher. The homework was insanely difficult, there was no extra material outside of lectures to aid understanding, and the structure of the class was fast-paced. In hindsight, the class was designed to weed people out of a small, competitive major, a fault which didn't lie with Walkow himself. Still, I hated that class even though I knew I loved and enjoyed learning about linguistics. This quarter, I'm taking Linguistics 120B (Syntax I) with Walkow, and my entire opinion of him and his class has changed. He was fair in Ling20, but he is clearly a syntactician with a passion for language and, as a result, is considerably more open a lenient with the class and his assignments. Certainly, the assignments are still rather difficult, but if you read the chapters for the week BEFORE the lectures and you do the problem sets in the chapters' ends (the workbook was immensely helpful here too!) you can stay on top of the course content with little trouble. I've realized over the course of this quarter that Martin Walkow doesn't want you to memorize notational conventions and PSRs to apply them to Language, but to actually tease out the peculiarities and flaws in the theory describing how Language works. In short, he is teaching you how to think like a linguist through the material, instead of simply teaching you formulaic theories to apply to data via rote memorization. Walkow's class is hard, there's no denying that (and many people think Syntax is boring), but he is fair with grades--including admitting his own mistakes in writing or grading the hw/exams--and is absolutely willing to help you fill in things you don't understand, provided you have done your best to do so on your own. If you want to learn about syntax and linguistics, and how to process data like a linguist, take your classes with him and Joe Buffington (the coolest and most helpful TA ever, who comes with the Walkow-class package). I thought for sure I'd hate this class and his teaching given the hell we all went through in Ling20, but he's a great guy, a good teacher overall, and a brilliant syntactician. I'd recommend him to anyone truly interested in learning linguistics---but he's definitely not for the faint of heart (and/or those who seek to "skate" through classes).