I've watched 3-7 on Blu-Ray. Have not made it to the others.
From those that I've watched Gatti's 5th was a surprise. I wasn't sure what to expect but, I really liked what I got. Nothing ground breaking, just a good understanding of the symphony and a great performance. The Boulez 7th was also a bit of a surprise. He gives an almost affirming reading. Not the icy Cleveland.
Ivan Fischer in the 4th is excellent. The 3rd, I'm sure, is the concert recording that is also available on SACD. Maazel's 6th is OK. Great playing, and something better than his Vienna 6th. It's heavy and powerful.
The visuals are top notch and the direction did not detract from the performance. The audio is good over all. I found the 4th and 7th to have better sound than the others.
One thing of note. The Concertgebouw has either a high turnover rate, or a very large pool of players. I've seen a handful of different principle players. Especially in the brass. Different sectional players through out. That was something that caught my eye.
It's too bad they didn't do this for the Leipzig Mahler Fest. That would have been a nice addition.