CS 61AS is a lab-centric class—there are no lectures. Students learn by working through guided readings and participating in discussions.
While some students find this format appealing, others may not. The CS department at UC Berkeley offers two other introductory CS courses, listed below.
CS 61A is the sister course to CS 61AS. It is offered in the traditional lecture-lab-discussion format, and covers the same Big Ideas as 61AS, except in the Python language and with a slightly different syllabus. CS 61A is the equivalent of Units 1-4 of CS 61AS.
Find out more about CS 61A here: http://www-inst.eecs.berkeley.edu/~cs61a/.
CS 10 is called "The Beauty and Joy of Computing". It covers the equivalent of Units 0 and 1 of 61AS, and also aims to provide a gentle intro to Computer Science. CS 10 uses a graphical language called Snap! that allows you to program by dragging and dropping components.
Find out more about CS 10 here: http://inst.eecs.berkeley.edu/~cs10/.
Each class has something different to offer. To see an organized comparison of CS 10, CS 61A, and CS 61AS, take a look at this document.