Fallout/Enemies

There are many, many critters that you will see in Fallout. They range from rats to super mutants to Deathclaws. This is an incomplete list, as there is quite a large number of creatures in the game.

Rats
Rats are relatively easy creatures that you will see in the beginning of the game.

Radscorpions
Radscorpions are closely related to the North American Emperor Scorpion, and have been mutated by the war. The increased size makes them larger than humans, and the venom contained in their tails can be used to make an antidote.

Humans
Range from varying (townsfolk) to medium (raiders, guards) to difficult (Brotherhood Guards) - note that they have no special. Experience earned is not dependent on the hit points and/or difficulty of the target.

FEV creatures & Ghouls
This is the direct result of what happens when a normal human is injected with the forced evolutionary virus. Extremely big and strong, Super Mutants make a formidable opponent. They are typically seen with floaters and centaurs, two creatures that the FEV can also spawn. (At least I think so...)

Tim Cain stated that ghouls were victims of radiation poisoning, not victims of the FEV virus on an IGN post. It turned out that the ghouls were former inhabitants of Vault 12 (where Necropolis is at). Vault 12's doors never functioned, therefore Ghouls are victims of radiation poisoning.

NOTE: I have found evidence that supports both approaches to how ghouls were formed: Either speak with Talius at the Boneyards or see what happened to the inhabitants of Vault 12.

The FEV was designed at the place now known as the Glow with hopes of creating a super soldier. The virus makes the humans stronger, but lowers intelligence and in its current state, makes them sterile.

Note: You'll only see Centaurs and Floaters in random encounters or in the first level of the Cathedral.

Robots
Robots - in a post nuclear game. They are either found in the Glow or in the two mutant bases. Pulse grenades do the best job, but plasma grenades and energy weapons should also do the job.

Creatures of the wastes
Creatures that wander around the wasteland, and don't fit under a particular classification.