Stuck!!

The Game: Castlevania (NES)
The Level: Last area of the Grim Reaper stage
The Brick Wall: The hellacious corridor leading to the game’s toughest boss is one of the meanest hallways in gaming history. If you miraculously survive the onslaught of Medusa heads and Axe Knights with all your Holy Water intact, you can use it to simply annihilate the Reaper (see video.)
Stuck-o-meter: High; this level will pulverize you, plain and simple. Your thumbs will weep blood.

The Game: Super Paper Mario (Wii)
The Level: Downtown of Crag
The Brick Wall: Hitting three blocks in a special order will open a door. The village elder insists you ask a very specific way - you actually have to type it in on a virtual keyboard. Nothing seems to work because the solution is to enter the same freaking word five times in a row like a nagging little bitch. Then, you have to write down a pattern 25 steps long so you know in what order to hit the blocks to open the door.
Stuck-o-meter: Medium-High; this is a frustrating low point in an otherwise excellent game. The fact that the solution can be easily looked up online is no excuse for crappy puzzle design. Skip to 4:20 in this video to see the magic happen.

The Game: Ninja Gaiden (Xbox)
The Level: Chapter 10: The Aquaduct (their misspelling, not ours!)
The Brick Wall: You killed the massive skeletal demon dragon, only to have your ass handed to you by a bunch of creepy little millipede bugs. Worse, they’re latching onto you, knocking you down… and the room is locked so there’s nowhere to go but the graveyard.
Stuck-o-meter: High; but then Ninja Gaiden is lamented by many a Ninja Dog for being too damn hard. Let this Master Ninja show you how it’s done.