I want classics.
[Some] people complain about the lack of new releases for 5e. This doesn't bother me at all, because I have hundreds... thousands... of adventures from previous editions of D&D that can be adapted to the new rules. Mine are hard copy, but increasingly you can get these gems as online PDFs (assuming you don't actually want to buy physical copies second-hand). And it's not that difficult to perform an adaption. It's easier to convert 1e/2e to 5e, and it's not overly difficult to convert 3e to 5e either.
However, it'd be even easier if I already had pre-converted demodands, yellow musk creepers, sons of kyuss, tasloi, aspis, lung dragons, su monsters, tritons, sylphs, nymphs, amnizu and kocrachon devils, babau and armanite demons, kopru, phanatons, decapus (decapi? decapuses?), bronze golems, skeletal tomb guardians (or bone golems... whatever... something with 4 arms), gorgimera, cave fishers, haunts, mujina, malferas, charonadaemons, juju zombies, dustdiggers, hellcats / bezekira, stone guardians, osquips, draconians, spectral guardians, guardinals, astral dreadnoughts, ascomids and derro.
You know... just to name a few.
Also, while you're at it, more named opponents at the upper end of the CR range. Avatars of the fiend lords (demogorgon, zariel, juiblex, anthraxus, fierna, etc), elder elementals, molydeus demons, linnorm dragons, spellweavers, whatever. The high CR creatures are the hardest for a DM to create, and yet some parties could be running into singular CR 20 opponents from about 13th level onwards. They can't always be ancient dragons, balors, pit fiends and liches.
With a Monster Manual 2, you've suddenly made my life as a DM much easier. I now have 500+ modules that can be converted in half the time, and vastly increased the variety of fun that my players enjoy. More spells and more magical items are always nice, but D&D is defined by the quality and breadth of its "rogues gallery".
