This one I definitely have to agree with Time because the album is really spectacular. 2009 was definitely the breakout of the Sludge-metal scene, the likes of Mastodon and Baroness really making a mark on the scene. Crack The Skye is a response to the electronic influences and crab-corey guitar stances that plague the hardcore scene as well as an alternative to angry bro metal like Lamb of God and such. Mastodon recalls metal's oldest influences: epic story telling and sweet album art, and really puts the hairy, beardy quality back in the scene.
While Leviathan and Blood Mountain were much harder albums, Mastodon keeps their signature sound while being much more accessible in this album to a larger audience. The album sounds great as a whole and even with 13+ minute songs such as the closer, "The Last Baron," Mastodon keeps it interesting. I also love the mix of throaty type vocals while maintaining an incredible sense of melody. Would recommend this album to most, and especially if its your first time hearing the band, Crack The Sky is a good introduction to their catalogue.