He was so damn good, as a songwriter and as a musician, but drink did him in. I was lucky enough to see him three times, each was incredibly fun. His compositions were so unique that some people overlook his ability, both on keyboards but especially on guitar. There's a bit from one of the videos of him playing live at a Boston Metro subway station (actually they are all worth watching, but...) where I think on the tune "Boom Boom Mancini" he does things on that guitar that are just astounding. But man, did he drink...
PS - was a challenge for his wife/partner, Crystal Zevon, who wrote a great book about the whole mess, "I'll Sleep When I'm Dead."