Hey Stu, glad to hear you're re-visiting Mahler and enjoying it.    I don't know all of his symphonies, though I own recordings of many/most of them, but the ones I am drawn to are the 1st and the 5th (with the 6th coming next).    Incidentally, I do agree with you that he is a slow burn, and tries for many (many!) things in each of his symphonies.   If I said otherwise in the past, I must have been drunk.   

So, in the case of the 1st and 5th , my fondness is mostly for the grandness, the massive sweeping romanticism (which yes, could use a little reigning in at times), plus the integration of (what I've always assumed to be) traditional Austrian folk melodies into the slow and scherzo movements.   There are some pretty thrilling moments in both 1 and 5, so give them a try sometime if you haven't already....of course, it's Mahler, so allow appropriate time.    #1 isn't too long, but the fifth is more typically interminable at (I think) around 90 minutes.  

Derek, thoughts on the Big M?

Not Mahovlich.