Because I’ve been listening to it quite a bit.
1. "Oblivion"—the highlight here has to be the solo section from 3:33 to 4:30. It’s very Rush-like in that it forms a distinct section of the song. I love how it drops into an entirely different timing and changes the song’s mood. It’s clear that Brent Hinds and Bill Kelliher put a lot of work into these shifting, building passages, capping the whole thing off with some dual string bends. It’s not your typical “solo over 8 verse riffs” sort of thing. I could listen to this section over and over again.
2. "Divinations"—this is the shortest, punchiest song on the album. The way the middle 8 takes the song to a new peak is cool, but the nicest touch is the subsequent lead in to the solo; a rapidly picked low E riff from 2:10 to 2:24 that foreshadows the solo itself. The choice of a fairly clean tone helps it pop out of the mix, making for a nice sonic surprise.
3. "Quintessence"—choosing a top moment is difficult, for this song is an embarrassment of riches. I’m fond of the weird sandwich of “these wild hearts run” stanzas between “let it go, let it go” parts that constitutes the chorus (first heard from 1:32 to 2:10). This section always reminds me of something Devin Townsend might come up with, because it betrays an inability to resist a catchy vocal line when it falls in your lap. There's also the doomy Taurus pedal part from 4:29 to the end that makes such a satisfying release from the preceding tech-metal explosion from 4:10 to 4:29. And this latter passage is my choice for best moment in the song. As I noted below, during my first listen to the album, this is where it became clear that Mastodon were as heavy as they ever were.
4. "The Czar"—Although Troy Sanders puts on a clinic with his bass lines in 'The Usurper' section, the riff that kicks off the next part, 'Escape,' is the highlight for me. On an album with dozens of fiddly, intricate riffs, this particular instance is refreshingly direct and classic sounding, Scorpions-like in its aim to rock. The riff’s reprise at 5:19 is all the sweeter.
5. "Ghost of Karelia"—not the most immediate song on Crack the Skye; it’s a solid “album track” nevertheless. The middle section from 2:37 to 3:15 really stands out with its punchy vocals and spiraling solo section.
6. "Crack the Skye"—lots of great vocals on this one, including a soaring Mastodonian choir, Scott Kelly from Neurosis in his customary cameo appearance, and some cool vocoder Cylon voices. Kelly’s cry of “momma, don’t let them take her!” is kind of the emotional peak of the song, if not the album, so that’s my choice right there.
7. "The Last Baron"—this song is just ridiculous. It would be cheating to pick the entire 13 minutes as a highlight. There isn’t a section that I don’t love, from the quavery acoustic intro with the melodies that stick in my head all day, to those 1-second guitar breaks before verses, to that lead line that creeps in at various points until the last time, when it charges onward into the concluding guitar solo. But the capper is the funky section at 8:19 that leads to the reprise of the intro and the song’s lengthy conclusion.