This album is beautiful. Unlike some later Zep albums, diversity isn't its strong point, but there is some very nice big ol' heavy, bluesy stuff broken up every now and then by softer acoustic things. "Good Times Bad Times" is a nice, almost-poppy, melting of the two to open things up, and "Babe I'm Gonna Leave You" (one of my favorite songs of all time) is a great combination. If you're not head-banging to its chorus, you're probably in a neck brace. "You Shook Me" is one of the aforementioned big ol' heavy, bluesy numbers, with a heavy electric take on that Delta melody-following-vocal-parts thing. "Dazed And Confused" (Conan O'Brien did a great version of this ;)) is a trippy, haunting, thing heavily based in the blues and another of my all-time favorites. "Your Time Is Gonna Come" is a slower, more acoustic number, followed by "Black Mountain Side", which is sort of similar but instrumental. "Communication Breakdown" blasts out after "Black Mountain Side", with a killer riff and just all around killerness, and the album closes out with two blues numbers: the slow "I Can't Quit You Baby", and the funkier "How Many More Times".
This is one of my favorite albums because Zeppelin did heavy blues so well, and they could diversify it (a la "Dazed and Confused" or "Babe I'm Gonna Leave You") and keep it sounding heavy, bluesy, and most importantly, heart-wrenching. Great music, and nice cathartic material to boot =).