I'm with Paul on this one. There are times when less is more.
I much prefer the current 5E single Monster Manual, followed by occasional books like VGtM and MToF that provide much more depth to the creatures in the game
Very much agree here. At the end of the day, I like more monsters, but I want monsters of quality. I would rather have a selection of well thought out monsters than a book full of generic weird concepts that are hard to fit in a campaign.
So in that respect, I've been a big fan of VGTM and MTOF, I think they are a great format for auxiliary monster books.
In terms of the 5e monster book, its a fine book, but to me it suffers two core problems:
1) Monsters at higher CRs are commonly overCRed. The game really does feel like it was designed for "easy mode" sometimes.
2) Monsters are often too generic, just relying on bland attacks instead of neat abilities and cool synergies. The "bag of hitpoints" often thrown at 5e is because of the core monster book.
Probably my favorite MM to date is 4e's MM3. 4e's monsters are interesting and unique, really creating synergies that make fight's dynamic and fun. However, 4e's core MM suffers from the "grind problem", monsters have too much defense and not enough offense, leading to many fights where the party is clearly going to win, but it will take another 4-5 rounds to end it. Solos in core 4e are notorious for this issue. However, 4e steadily improved on the design in MM2 but perfected it in MM3. MM3 monsters are interesting and offensively focused, finally solving the issue and leading to some very cool monsters.