I'm one of the biggest Guns N' Roses fans in the world, and basically started playing guitar because of Slash, but I was a little underwhelmed. Not because it wasn't well written -- that wasn't the case -- but mainly because Motley Crue have already done the definitive L.A. metal autobio.
While I'd rather listen to GNR in most cases than the Crue, I rate "The Dirt" higher than "Slash" for a few reasons.
One, it came out first, and completely raised the bar for tell-alls about sleazy metal band behavior. There have been other books about bands raising hell -- the Led Zep bio "Hammer of the Gods" is probably seen as the standard bearer -- but most of those books, "Hammer" included, face some serious challenges to their authenticity, none of which have been leveled at Motley. Frankly, if it hasn't already, "The Dirt" is probably going to replace "Hammer" as the one that critics refer to most often in the future for a while when referencing historic rock debauchery.
I'm not saying that the Crue seemed crazier than GNR, did more drugs, drank more drinks, etc., but other than his alcohol intake at the peak of his alcoholism (almost a gallon of vodka during the day followed by shots of whiskey and beer chasers all night), there wasn't much that made me raise an eyebrow Slash's book.
Also, the Crue tome is also more effective in that it presents the perspective of each member of the group, whereas Slash's book is a more conventional autobiography that just has his take on his career. Slash deserves a certain amount of credit for noting that Axl has his own take on things every time he blasts Axl's selfishness that ultimately led to the demise of the band in everything but the name. But I was left wondering what Axl would have said...or what Steven Adler or Izzy Stradlin or Gilby Clarke would have had to say.
Another disappointment is that you get very little insight into the music, beyond some of the obvious stuff ("My Michelle," in case it wasn't obvious, is about a girl whose dad worked in the pornography business and mom o.d.'d. But you probably already knew that if you had ears to listen to the music or eyes to read the lyric sheet). Even though Slash wrote a lot of the music, it's not necessarily too informative to read something like "Me and Duff wrote that one while jamming in Chicago," or whatever. I guess that for the most part we'll have to wait for Axl's book...hope it comes out faster than "Chinese Democracy."
One interesting tidbit in this area though is the origin of the "Where do we go now?" bit in "Sweet Child of Mine" coming from a discussion in the studio of where to take the song, not of, say, where the relationship with said girl might be headed.
All that said, the book accomplishes what Slash set out to do with it -- set some memories to print in case he forgets them later, and explains to all of us the hassle of dealing with Axl Rose and thus why we shouldn't ask him "dude, when are you getting the band back together?"