Cursory analysis can be so provocative; can I try?
A bitter genius whose compositional long-windedness was necessary and natural, unlike Bruckner's which was an affectation derived from his man-crush on Wagner. There's more meat on the bones of his symphonies than he's often recognized for, especially given that moderns almost exclusively listen to his compromising, and often terrible, more commercialized nationalist output; as with any composer you should be listening to the pieces that their public hated, to really get a feel for their work.
Also, let's not forget that Mahler being "overrated" is a very
recent phenomenon, spurred almost entirely by the athleticism increasingly associated with American orchestral playing in the last 20 years (Bernstein's boner for this composer also contributed to his subsequent enthronement in "educated" circles). As such I don't really think it's fair to say that Mahler is generally overrated; most people don't, and didn't like his music, and the only reason it gets so much air time is because the players and conductors control what the public hears in classical music to a large extent, and Mahler wrote music catering exactly to the interests of that demographic. It's easy to mistake this for real "enjoyment" in the non-musician public.
This shit's tight:http://www.youtube.com/watch?v=60PGX0RzUvU
Check out symphony 2 also. But what do I know, right?