Pro: One of the most influential and innovative folk musicians of the 1970s, Martyn introduced elements of jazz and blues into his sound: without his classic albums Bless The Weather and Solid Air, it's arguable that there'd be no Tunng, Four Tet or even Portishead.
Con: He's also responsible for the plague of guitar-tapping, loop-pedal-wielding idiots who batter our ears in the name of folk. Thanks, Mr Martyn, for Newton Faulkner.
Pro: Martyn can be a terrific live performer, with his gruff Glaswegian vocals, innovative guitar work and experimental flourishes captivating audiences. Check out his landmark Live At Leeds album for evidence.
Con: He can also, if not in the mood, be prone to a pretty bad gig. Perhaps the epitome of hit or miss, his performances can veer more towards curmudgeonly than classic.
Pro: John Martyn is a battler: he's suffered a leg amputation, alcoholism and the loss of many close friends, including Nick Drake, but never even looked like quitting. For a man of his condition to still be performing is remarkable.
Con: Unfortunately, diligence and recovering from horrible setbacks doesn't always make great music, as the story of Def Leppard confirms. And there is something a bit 'last chance to see' about watching Martyn now.
Pro: Martyn is an artist's artist, with many greats including David Gilmour, Eric Clapton and John Paul Jones lining up to work with him.
Con: He's also worked with Phil Collins.
Pro: He's great at cover versions; his takes on the likes of Portishead's Glory Box, Billie Holiday's Strange Fruit and Singin' In The Rain are right up there with the original versions.
Con: We don't know about you, but seeing a 59-year-old bearded bloke singing: 'Give me a reason to be a woman, I just wanna be a woman,' is a bit, well, wrong.
Tues, Jul 15, The Grand Theatre, 46 New Briggate, Leeds, 8pm, £ 25.50. Tel: 0844 848 2706. www.johnmartyn.com