I have the First, Third, and Fourth editions. The Third edition was my introduction to backpacking. I memorized almost the entire book. Found the first edition in a used book store, and snatched it up. The advice is exceedingly sound, except for the details about gear, of course (things have changed a bit in 40+ years.)

The 4th edition with Rawlins is really very good. It can get a little choppy as they switch between the two writers, but the gear advice is excellent, and the how to and "why to" (mostly from Colin) is still a great read.

Buy the book, Grasshopper, and learn from the master.