Michael, I just bought this not too long ago, but have not gone through the whole box. That said, I really do like his M3, M4, M6 and M8.
If you like slow, detailed, philosophical performances (except his M6, which is faster) than you will like Maazel. I like him for these very reasons. His M8 is my top M8, but I stand alone here! His M3 is in my top 5 for M3's.
Most people will advise you not to get this, but I feel Maazel is a unique Mahler interpeter. Not for someone new in Mahler, but a good choice if you want to head off the beaten path.
--Leo