Death Magnetic is not that bad musically. But Rick Rubin butchered sound of that album. Loudness war at its worst. Guitar Hero version of songs sounds better than original CD...
At this point, I wouldn't doubt if they took an additional six years to put out something new. Not counting Lulu - because no, it DOESN'T count as a Metallica album, and never will - it's already *been* about 6 years since their last album.