I can give you plenty of reasons why, but it's typically easier to explain what the issues are with an album than it is to go into detail about every successful part of it, even with bad albums. But hell I'll give a brief summary of what I love:
Blackstar- the switch from the incredibly jazzy and chaotic instrumental into the heavenly and soulful bridge section where Bowie goes full crooner is beautiful and seamlessly done.
Whore- The horns get more chaotic as Bowie gets more abrasive with his voice, hitting high notes that sound just a bit rattly which echoes his breathing across the track really damn well. It feels desperate, as it should.
Lazarus- I don't even know where to start with this one. Highlight of the album, gorgeous verses, the horn is so somber across the track, and the two note riff at the end feels like death approaching (the "I'll Be Free" refrain is icing).
Sue- Probably my least favorie on the album, but it has a manic energy that doesn't let up through the whole song, and the aggressive breakdown at the end of each verse is fantastic.
Girl Loves Me- WHERE THE FUCK DID MONDAY GO. There's also a really dark contrast in this track instrumentally that I just love, where it gets really pretty and light before falling back into a very dark, robotic groove.
Dollar Days- It's a strong ballad, lyrically one of the high points on the album. Sounds a lot like something from Space Oddity.
ICGEA- The harmonica from Low, the saxophone that echoes Bowie's first instrument, and the verses themselves that perfectly encapsulate the theme. It's the perfect end to his career and his life.