I find his early works much easier listening, it's mellow jazzy music. I've been spining Closing Time (1973) and The Heart of Saturday Night (1974) for the past two nights. I think from Swordfishtrombones-onward he began to take his music into a more avant-garde direction. His first few albums were on the Asylum label, I think when he jumped over to the Island label he began to produce his own music, hence the freedom to experiment.
He sure has a heck of a voice on his early albums, before he drowned it in whiskey and cigarettes. I found this video of him on Letterman...and whether you like his voice or not (or are in the Tom Waits mood :p ), you have to give him some appreciation for his stage performance:
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Quite the contrast from this:
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