Ah, the Monstrous Compendiums.
Alzrius has been playing about as long as I have. When I got into the game, it was also initially through the Black Box, and I moved on to 2e because it soon was the only thing available. So I'm more familiar with the MM and softback MCs than the binder experiment. I've looked over all the MCs recently, and honestly, they aren't all that impressive. The MM combined with the MC Annuals, especially Annual 2, is a much stronger monster collection IMO. It's weak on extraplanar entries, but the first Planescape MC mostly covers the gaps (MC8 originally did that but the XP Values in there are very badly inflated). Of course, of the 3 MCs missing on DriveThru, 2 are Annual 2 and Planescape 1.
I don't know if we need to get to much into the binder problems here, but there were the two big flaws. First the pages were too flimsy, they had to be torn out of the package, which sometimes ripped the binder holes and they weren't particularly durable. Second was the alphabetization scheme which fell apart after MC3. Both of these problems are less an issue today with the pdfs, where the entries can be printed out as needed.
Anyway, I pretty much agree with Alzrius' assessment here of MC1. There's too many questionable entries, too many full page animal entries, and too many missing monsters, not even getting into how demons and devils were yanked out. I think though that 1e MM entries were prioritized here. From my own examinations of 1e and 2e monsters, MCs 1-3 generally seem to be about updating material from 1e's MM and MMII. The FF has a lower priority and seems to have more focus with MC5, and later a good portion of it was updated in MC14.That's probably why MC1 is missing stuff like the drow (originally GDQ1-7, then Fiend Folio) and the aboleth (originally I1 then (MMII). The aboleth in particular maybe wasn't really a big thing back then anyway, I think they didn't hit the big time until Night Below. Anyway, it's not surprising that many 1e players were pissed with 2e. To me it's no big deal because I have the MM, the four Annuals, the three Planescape MCs, and the Mystara MC in print which make for a pretty solid monster collection. But back in 1989, this must have been a letdown.