The problem - or one of the many problems - is that law schools, or at least law professors, to a large extent act as if their students are already lawyers. Classroom lectures are often indistinguishable from water-cooler chit-chat among law firm partners. This makes them interesting, but also useless for the uninitiated.
As with water-cooler chit-chat, however, you don't need to be expert to follow along and benefit. You just need enough of an understanding of the fundamental principals and terminology that you have something on which to hang all the apparently semi-random things your professor will say during class.
Same thing (IMO) for case readings. Reading the cases in depth before class is incredibly time-consuming and usually an exercise in frustration. Instead, you might try just scanning the cases before class, or even reading a bit - but stop when your understanding is being taxed. Don't try to understand the case ahead of time. Instead, use your pre-class reading as a familiarization process to help the class lecture make sense. Then, if you want, you can go back and read the case after class, when it will make sense (and go faster as a result).
The bottom line, for me, is that the standard law school reading materials don't give you what you need to teach yourself the law. This is the opposite of many subject in college, where one could (and I often did) skip all the classes and do well on the exams based entirely on the textbook. I would not recommend this for law school (believe be - I tried it). You will drive yourself batty trying to extract anything useful from the casebooks by yourself.
On the other hand, the lectures alone are useless as well. You must be prepared, and that means reading the materials. Just don't overdo it.
/as with all things, everyone is different. find your own way.