Halo 3's Cortana
Oh man, where to start. Any level that looks like a series of sphincters better not be full of s**t, but this one is. FPS games are at their best when you're weapons feel powerful and you feel like a hero. In this level you're weapons do nothing but tickle these enemies, and when the enemies look like cling-ons inside an anus you wonder what issues the developers were dealing with when they designed this. All the fun of Halo is taken away as you blast hordes of scuttling rectum-dwellers instead of awesome alien warriors. Eventually you get pissed off and try to run past them. The level is long, but you finally reach the end where you realise......you have to go back out the same way. This time there's more of the enemies too. This is easily the number 1 worst level of all time.
Tekken 6's Nancy-MI847J
Sure, fighting the greatest martial artists from around the world is cool, but what I really want to face is a giant robot crab that looks like its made out of meccano. Hopefully I have to constantly sidestep around it like a lonely loser attending a dance class for the first time. Maybe it could have a giant health bar and missiles that make it stupidly hard to beat while simultaneously teaching me none of the skills I need to learn to get good at the game. Bravo Namco, you've done it again!
Alone in the Dark Central Park
So much potential. The opening parts of the game see you struggle with the awful controls and the innovative but broken inventory system. You struggle through numerous insta-death situations escaping a building that is being torn apart by a hole in reality. Its kinda cool. You escape to the park in a car chase which again has terrible controls, but the tension and pace of the game keep you going. Then you get to the park, where you will spend the rest of the game. Dull, ugly and repetitive, the game settles into a slog of terrible inventory management and awkward combat. Here's a tip for developers, if you want to have very difficult driving sections, don't have them happen in a park. They're full of these tall, immovable things called trees which kinda get in the way.
Had to include this one as its popular with all you guys, and by popular I mean hated. The design is incredibly lazy and ugly and the enemies are the same ass-goblins you fight in Halo 3's Cortana level. It almost seems like the developers were told the game had to be a certain length and some guy knocked this up on his lunch break to pad the game out. If Halo was a delicious steak dinner, this level was the soggy side salad.