The following Fiends in particular are noteworthy for being written up as little mini-dramas reminiscent of EC comics or Clive Barker stories:
Russ can draw us scarier."
The scripted approach may be friendly to the inexperienced adventure runner, and was eventually the way D&D would go under the influence of Greenwood and others, with monster ecologies and tactical notes. But it also leaves little room for creativity, or for surprise if the players have read the monster book. To innovate, the DM has to write over already-written-in space, rather than project into blank space.
I will go further and say that Greenwood's criticism misses the mark. The bad monsters in AD&D are bad not because they are under-described, but because they are misconceived in the first place. If you need any proof, behold the abundance of uninspiring and ridiculous monsters even in the 2nd and 3rd edition epochs, where the norm got close to two full pages of stats, description and ecology. And in the Fiend Folio, no matter how much detail you give the flumph, how much we know about its gizzard and egg sacs, it's basically a little flying saucer alien out of place in a medieval fantasy world it never made.
Well, I guess the point of diminishing returns is here. There were some other worthy creatures in the Fiend Folio - the kuo-toa and drow (though here, also over-written; most of their surprising abilities and details should have been kept in the original modules, for the above stated reasons) - the iron cobra - the githyanki and githzerai - and a decent roster of b-list humanoids and critters for weird worlds without orcs and minotaurs.
And a whole sackful of clunkers. Can they be rehabilitated? We'll see, in the weeks to come.