This feature I really looked forward to! The monsters don’t give away way too much information about the world, which will luckily keep most theories (about the Corruption, Crimson etc.) going and leave some mistery to the players.
The Zoologist and the Golfer both look really cool and I already have some ideas for their housing.
To sum it up: Really nice mechanic, with the bestiary you‘ll get a small reward for discovering the many creatures and it will be fun to complete it! The entries also really remind me of the Pokédex entries, which is also amazing.