List of enemies
Important! This list contains only those beings (intelligent or not) which are hostile towards you by default. Rest of the population is usually neutral or friendly, however obviously this change as a result of your actions. You should also know that some of the creatures (including mirelurks and supermutants) appear in different forms.
Legend: NAME - name of a creature or of a group of creatures; ADDITIONAL INFO - a short description of what you should expect and how to react; THREAT - threat level on a scale from 1 to 10 - in many cases these values vary depending on types of enemy units.
The game world is populated only by five of these creatures and obviously they're extremely difficult to kill. Avoid melee combat at all costs and use a fatman, a rocket launcher or a minigun to kill them.
Nothing you should be worried about. Just make sure that you're not moving towards them in a straight line and you should be fine. One hit from almost every weapon should do the trick.
These monsters are very easy to kill, as long as you avoid the acid. Use a shotgun or a hunting rifle to kill them.
These beasts are extremely powerful and they can rip you apart in a manner of seconds if you allow them to get closer to your character. Aim for their legs in order to increase your chances of success.
You don't have to worry about the turrets too much. Some of the devices are equipped with rocket launchers, but the good news is that you'll need to fire only a few shots to destroy them. You can also search for security terminals if you want to disable or reprogram them.
For most of the time they're not using any weapons, however you may also encounter armed scientists. You shouldn't ignore them, because they may be carrying plasma pistols.
The good news is that Enclave soldier won't appear unless you've been to their base. Watch out for soldiers equipped with powerful armors and weapons, including plasma rifles.
For most of the time you'll be dealing with the weakest kind of feral ghouls and in this case 1-2 shots will be more than enough to kill them. You must watch out for the glowing versions, because not only they're more powerful, but they can also harm you with large doses of radiation.
The "standard" ants are fairly easy to kill, even if they take you by surprise. Fire ants are much more dangerous, especially if you allow them to get closer to your character. Use grenades or a sniper rifle to kill them. And don't forget about the queen! :-)
The differences here can be quite significant, depending on the type of creature you've encountered. You should know that mirelurks have a very strong armor, so you should use heavy guns or explosives against them. This is very important when you're fighting kings of hunters.
Gutsy is one of the less pleasant robots. Not only it's hard to kill, but it's usually equipped with a flamethrower or a plasma rifle. As a result you must be careful while trying to get rid of it.
Molerats are relatively easy to kill even if you're starting the game, however you must acknowledge the fact that they're very fast, so they can jump at your throat in a manner of seconds. Use a ripper or other melee weapons to hunt them down. Remember that Moira can sell you a weapon used to kill these creatures.
Most of the protectrons are fairly easy to dismantle. You may have to spend a little more than time than with robobrains, but still it's not a big deal. Use the fact that they're very slow.
You'll be dealing with these small insects while exploring crypts, sewers and other types of tunnels. Don't waste your ammunition on them. Instead use a melee weapon.
Radscorpions are somewhat similar to mirelurks, because their cuirass can withstand a lot of damage. You should also know that they're very fast and that they can poison you with one hit. I would recommend running away, especially if your character isn't strong enough.
There are many raider fractions populating Capitol Wasteland. The weakest groups are only equipped with pistols and melee weapons, but you may also encounter raiders with sniper rifles or flamethrowers.
Robobrain is one of the weaker types of robots. They usually carry laser guns, but the good news is that they explode after a few hits.
This is by far the most dangerous version of the mechanical adversaries. Sentry bots are equipped with some of the most powerful weapons, including miniguns, flamethrowers and rocket launchers. You must be extremely careful while trying to eliminate them. Don't forget to use EM mines or pulse grenades!
Most of the slavers should be neutral towards you by default, however there are exceptions (for example - in Evergreen Mills). Use a combat shotgun to kill them or a sniper rifle if you want to attack them from a distance.
There are a few species of supermutants. When you're dealing with the weakest kind you may even consider using shotguns. Brutes and masters on the other hand will require you to use your best arsenal.
Talon Company mercenaries
I guess you may be surprised to hear that they won't be easy to kill, because they'll appear even very early during the course of the game and you'll also be dealing with groups instead of single soldiers.
You may encounter hostile Vault citizens if you decide to visit other crypts located in the Capitol Wasteland. Thankfully, they're easy to kill, even if you're dealing with a lot of them at the same time.
I guess you may have some problems with the dogs, especially early during the course of the game, when you're using standard armors. When you get stronger they become almost harmless and one shot will be more than enough to kill them.
Yao guais are an apocalyptic version of bears. These creatures are only slightly less dangerous than deathclaws. They've very agile and they can inflict massive injuries if you allow them to get closer to your character.
Behemoths are the strongest creatures in Capitol Wasteland. Thankfully you'll only meet a five of those during the game.