I am a very big fan of Hunter S. Thompson, and have read both Fear and Loathing in Las Vegas and Hell's Angels.
I really enjoy the way he writes. His style is nowadays so often imitated- but NEVER equaled.
--Now, first a Warning--
If your only other experience with the late Dr Thompson is Fear and Loathing in Las Vegas, and you got into all of the mindless drug fueled debauchery in that, well I have bad news:
F&L on the Campaign Trail is NOT that at all, so if that's what you are expecting then you might be disappointed. Instead, read Hell's Angels first. It still has the sex and violence, but it reads more like real journalism than someone narrating an orgy. That will at least prepare you for what to expect in Campaign Trail '72.
If you are into politics at all, this is a MUST read. HST really goes into all of the intricacies of the electoral process, but does so with such flair and style that it never becomes dry.
My personal favorite Thompson book is Hells Angels, but I'd have to say this one comes in a close second.