So I started thinking about the games I usually run:
- Talislanta: tons of beasties, but I mostly use the races as the badguys
- D&D: lots of monsters, but I tend to only use a few
- SLA Industries: Carriens, Carnivorous Pigs, Manchines...the occasional weird thing I make up or convert from somewhere else (occasional meaning approx once in 10 missions)
Then I started looking at games I used to run:
- Vampire: Humans, Werewolves, Mages
- Werewolf: Humans, Vampires, Mages, Werewolves, Spirits
- Mage: Humans, Vampires, Werewolves, Robots, Demons
- Blue Planet: the occasional Aborigine
- Star Frontiers: Sathar, the occasional alien creature
Am I just slacking as a GM?
I remember running a game of D&D where the big bad was a werewolf, and there were a few zombies; in another campaign the baddies were all orcs, a couple of wolves and a bear.
Another campaign I ran took place almost exclusively, around 80% of the campaign, was inside the city walls of Greyhawk, and even outside the city walls I vaguely remember a goblin patrol; and another the only non-PC race badguys were some trolls and deep dwarves.
I guess what I am trying to say here is pretty simple, you do not need a ton of creatures to make a fun campaign. Having 1000 different monsters available is not going to make a difference if you are only going to use 4 or 5 of them.
Also, it seems it would crowd the world.
Next time you create an adventure for your players, think about this: if the villain, or big bad, is not required to be a different monster, keep to something you already have. If you really, really want to use a particular monster, think about the ecology of the creature and how it will fit into your world as a whole, if there is one, there are bound to be more.
Looking through various forums and adventure modules it seems to me that people will use what is available without thinking about using what they need.
Do you really need an Illithid at the head of a Saughin cult of the squid god? Why not just use a regular Saughin, boost its power and give it some minor spell-casting ability? Otherwise, you are having to not only fit the Saughin into your campaign world, but also the Illithid.
Just some thoughts and rambles, enjoy your game.