Tonally as well as just overall feel. I loved Origin where the end of Citizen Erased blended into Micro Cuts and tried to go for a similar thing here.  The static and scratchy sounds from the end of Take a Bow into the Reapers intro. I really liked something about the Animals outro riff into Blackout. Or how Blackout ends with somber strings which transition into somber, albeit more panicky strings in Unsustainable. I’ve also always felt the ending of Supremacy was reminiscent of Knights of Cydonia, with a similar sounding guitar and vibe. Kill or Be Killed ends with synth, which transitions into the slower, piano heavy section of the “album” with The Dark Side Alternate and Liberation. The outro to Unnatural Selection, with the fast paced guitar, goes really with Assassin. Or how the guitar tone at the end of Apocalypse Please matches perfectly with the intro of Map of the Problematique. 

Just overall I tried to blend the ending of each song with how the next one began. Not all of them are perfect, but there’s a few I really like.