10 One-Off Video Game Levels That Totally Change Everything
2. Xen - Half-Life (1998)
There was no way a game as revolutionary as Half-Life would end in a 'normal' way. It does go for the final boss option, admittedly, but the setting for that battle and the whole level preceding it is an experience quite literally lightyears away from what you've been doing up until this point.
An experiment at the Black Mesa Research Facility goes wrong, summoning hordes of hostiles aliens to Earth from the planet Xen. Armed with a crowbar and an HEV suit, Gordon Freeman must work his way through the lab in order to dispose of the alien invaders and undo what has been done.
The closing act of the game involves stepping through a portal to Xen itself, and from there, things just get crazier and crazier.
Gone are the battered hallways and splattered scientists of Black Mesa. Instead, what lays before you is a daunting expanse of precarious rocks, organic-looking caves and a stunning space backdrop as far as the eye can see.
In this area are sights you've never seen before, including the hulking headcrab matriarch, the Gonarch, and the otherworldly final boss of the game, the Nihilanth.
And while the mechanics of this level aren't exactly beloved by everyone, the abrupt switch-up from run-down research facility to full-on alien hellscape isn't one your mind is going to let you forget.