I havent found any answer in the forum now, so I take up this question from Red:
"Is it better to spawn monsters in certain places only (like dungeons), or should there be an option to let them spawn at the surface (e.g. at night)?"
There should be hotspots like old ruins, castles, pyramids or temples, where are just specific monsters which guard loot which you can find there. It would be nice if this loot is also placed in the world on shelves and other surfaces and are not just inside chests.
The strenght and amount of these monsters should be as much as worthy the loot is.
These ruins and ancient temples should be very rare and variable in size and complexity, that they dont get boring. and some have a secret entrance to a cave system inside for further exploring.
But smaller ruins with some pilars and huge stones/bricks and bolders and old buildings could be more often with not that many enemies and just basic loot. A certain amount of varity is the key and especially different buildings and ruins in different bioms.
But nothing speaks against a option to let them spawn everywhere but not as standard.
Maybe in the water could be huge sharks which are friendly but they should show interest in the player if he swims and a minimal chance of getting bitten or even hunt down.
Beside that the bandits at night in the Java version was nice, but monsters everywhere could be a little bit nerve-racking, espcially if they spawn at the base.