I did LEEWS before my 1L year, and it was helpful, but it wasn't a magic bullet. Breaking things down systematically is important, and writing in a way that makes it easy for the professor to find all the items he's looking for is equally important. I disagree, though, with his narrow focus on black-letter law. Professors really do care about all that other "fluff" they talk about in class, and it comes up in subtle and sometimes not-so-subtle ways on exams. LEEWS teaches the elementary technique, but to do really well, you have to pay attention to what kind of analysis interests your individual professors. I learned that after my first semester and got significantly better grades my second semester.
While we're on the subject of exam strategy aids, I also recommend the book "Getting to Maybe." It helped me with my writing style on exams and helped me to come up with arguments during exams. The book is focused on law school exam-taking, but in a way it's also a nice introduction to thinking like a lawyer.