So as I am thinking about my new campaign world of Moithane, I've come to the opinion that this is a new world, with a new game system, and there is no need to preserve old tropes, although old tropes are welcome if they work.
So, what do I do about all the monsters? I'll probably play them a lot like they have traditionally been played, but I also have a chance to do new things with old monsters, as well.
One consideration is that Moithane is a ringworld, and therefore can support huge populations of each type of monster, many more than a traditional fantasy world could support. (How many ettins are there in a typical fantasy world?) Of course, one area would only have so many of each type of monster, but there could be an entire continent of a monster type that is normally quite rare.
The PCs are starting out in a relatively "normal" part of the world, with elves in the forest, dwarves in the mountains, humans in the cities, halflings whereever I can fit them.
One difference is that the area has orc amazons, although they are good at hiding so most people don't see them. In fact, orc amazons are so good at hiding, even they can't find themselves.
Another thing I plan to do is make templates for nymphs, dryads and sylphs. Nymphs based on humans and elves would be the most common, but you could have a dwarf nymph, an orc nymph, or even an ettin nymph. I also might make nymphs a lot more powerful than they are in the Monster Manual, although the MM type could be retained as a sort of "nymphette". The concept is that nymphs are immortals who are worthy of worship in their own right.
I decided to start this thread to see if I can get any other ideas to tweak the monster tropes a bit.