First three albums and 4 of the 5 after he got out of jail are all fabulous albums. The others may not lack the consistency but they still contain enough strong songs to justify investigating. First time heard version of 'Billy Austin' on "Shut Up.." was stunned such a haunting performance.
Might want to check out his biography "The Life and Near Death of Steve Earle" by St John; certainly a very flawed if captivating personality and gives a lot of his songs some perspective and quite an eye opener about his life and personality. Altered my opinion of Lucinda Williams and Del McCoury quite a bit, and just reinforced my opinion of Emmylou.