Difficulty Spike: The Colombian jungle. Terrorists concealed by bushes that they can see through fine, assault rifles come into play, and as mentioned above in Demonic Spiders, they can magically see you and lob perfectly-timed grenades over hills that you didn't even get close to. After you're done with it, though, the difficulty (or at least the Grenade Spam) drops back again until Kamchatka, near the end of the game.
"Funny Aneurysm" Moment: One of the levels has Saddam Hussein in it (he only appears in a cutscene), through cheats however, you can spawn and kill him. Now try to play this game now that Saddam is dead for real.
Narm: Most of the dialogue and voice-acting in Payback is so ridiculous and over-the-top that it's almost impossible to take seriously.
Some of the first game's death sounds and animations.
The Big Bad's death in the first game. Despite getting ripped in half by falling machinery, the only sound you hear is his death scream.
Nightmare Fuel: The slaughterhouse in the Sudan mission in the first game and the village of Pureza in the second game.
Sequelitis: The third game. No John Mullins, different developer, different story.
That One Boss: The final boss of the first game is regarded as this by many, with an extremely powerful weapon, nasty turret back-up and being absurdly resistant to everything with the Handwave of "he's wearing body armour".
The Interrogator in the Hong Kong prison in the second game, with his near-instant-death machine gun. And he's Made of Iron even though he doesn't wear armor.
The Final Boss in the second game is an attack chopper that rip you apart in seconds and takes an INSANE amount of ammo to bring down if you don't know what you're doingnote shoot the engines' outer panels and their glowy insides until both catch fire like in the hospital, and then shoot the pilot. This is the one time where the OICW's alternate launcher actually comes in handy, as if you can adjust the range properly, you can lob grenades at it safely and defeat much faster then you would with normal ammo.