1) Fort Frolic - Bioshock
God I love this. personally I think is the most exciting section of what is quite plainly a classic. It had everything. A sense of elegance, a sense of madness, visual and metaphorical decay and some of the most messed up characters in the history of videogames. Still, what do you expect from the guy who designed "The Cradle" from Thief?
2) 2Fort - Team Fortress 2
Come on, I dare you to think of another level that is so perfectly made and so well balanced on an online game. Go on, do it. Don't worry, I can wait all day while you do. I'll be playing this, over and over and over again. Nothing compares, nothing comes close. It's the beauty of 2Fort.
3) Ravenholm - Half Life 2
There's just something so... upsetting about Ravenholm. As you wander it's dark streets, fighting the zombie hordes, avoiding the traps set by the quite frankly mental Father Grigori, you can't help but realise that everything you've fought for, everything that everyones fought for, could be so easily destroyed in such a brutal way by the viscous combine... Classic stuff right here.
4) ... Everything - LittleBigPlanet
See that? Everything inside that little box is complete genius. Every single little iota of it, is professional, polished and just damn fun.
5) Hanger - Metal Gear Solid
This one may be just me but.... When you first stepped into the hanger on the PlayStation version of Metal Gear Solid... you just knew you were playing something special, something fresh, something unique. It's always going to be one of the best moments in gaming for me.