Demonic Spiders: The burned zombies in the final area, weak melee enemies that explode when killed.
Goddamned Bats: The ghosts. They show up on the surface, and they spawn whenever Albert steps into sunlight. You can't melee them, so you have to waste bullets shooting them, and their unpredictable movement makes this much harder than it needs to be.
The cannibal giant can only be hit after he throws his spiked shield. To avoid the damage from the shield, you have to make sure it hits an obstacle - it's otherwise completely undodgeable. After he throws it, you can shoot his weak spot, the giant target on his stomach. He moves too slowly to really catch Albert, so you're not in a lot of danger from him, but he has a mountain of HP and you're struggling to chip it away.
Junk Thardus's weakspots are not always obvious, and it has several phases. While its attacks are fairly easily dodgeable, for some ungodly reason, the devs saw fit to shut off your healing for this fight. Even worse, its second phase spawns ghosts, and its third phase gains an ungodly fast shockwave attack.
The Saboteur requires you to stun him by shooting out the generators in the boss arena. This is easier said than done. Every time you shoot out a generator, it needs some time to recharge, and the saboteur can shoot them to stun Albert. Even under the best of circumstances, the boss stunning only works about half the time. All the while, the saboteur is running around the arena blasting at you with his Hand Cannon.
Albert's reaction to discovering that the first surface world was actually another underground facility was quite appropriate. But the reaction was still devastating hilarious when it was meant to be dramatic.
The two vaults are called Glory and Fist.
The screaming enemies that jiggle wildly before exploding.
Nightmare Retardant: Most of the mutated enemies are supposed to be scary, but the models look cheap and fake, their AI is terrible, and they attack by hitting Albert with goofy, clumsy slaps, which don't do anywhere near enough damage to make them a threat.
The Scrappy: Albert is a remarkably unlikable main character. While some of it was probably intentional given the game's plot, he seems less like someone you could Love to Hate and more like a rude, dim-witted loser.
Shocking Swerve: The reveal that the "surface" is in fact just a larger underground vault, with many of the buildings in it being nothing but facades, raises the questions of 1) why some of the buildings aren't facades, 2) where the cannibals came from, and 3) what possible purpose the city could serve that Glory couldn't perform itself.