This sounds even better than the German radio broadcast you find a while back. I'm going to wait for Fischer's Mahler box before buying any of his CDs. As far as complete Mahler cycles recorded in the 21st century so far, this might be the best one. It's mostly better than Stenz, Zinman, and Nott, and it's shaping up to be better than Vänskä's hit-or-miss set. And it's certainly better than Gergiev's... And if only Fischer's brother's cycle had an 8th I would mention that as its prime competition.
I'm on the fence with the M9 however, but I totally understand why you like it. His tempos are just right. The playing in the inner movements isn't that great, but he has one of the better first movements I've heard in a while. The thinner sounding string section shouldn't be the issue that people are making it. It's not lush like Berlin, but I'd say it's similarly "thin" to the Czech Phil, a great Mahler orchestra. Every orchestra just has a different sound, and I find Düsseldorf's to fit Mahler's music quite well. Particularly the woodsy winds (à la the BRSO) and the dark-hued brass sound.