Never heard of Michael Riedel, but it sounds like a great performance! I've only heard the second symphony once, in Malmö. It was sadly enough quite sloppy and unfocused with not enough passion. My greatest Mahler experience ever is probably the 8th in musikverein with Boulez. Another great was the third with Bychkov, also in Vienna. Mahler live with the Concertgebouw orchestra must have been fantastic!