Allow me to give you the quick-and-dirty of this manga.
10 chapters in total. 2 chapters are cannon sequels to the original BLAME! manga series. #6 'Netsphere Engineer' & #8 'BLAME!²' are those two cannon sequels.
Everything else is a mix of parody, dark (often body horror) short-story, or something else entirely.
5/10 for the whole thing. 10/10 for the 2 BLAME! sequel chapters.
If all you care about is BLAME! and cannonically-relevant material to the manga, check out the two chapters listed above. If you're a die-hard fan of Nihei's work, well obviously the entire thing is worth it. If you don't fall into either of these two
camps, this manga is mostly a 15 minute time sink (yes, you can burn through it that fast) that probably won't do anything for you.