[MrFlibble]

Sorry for bumping this, it's just that I didn't realize that the Duke Nukem Forever side-scroller reached any stage of playability during its development until having taken a closer look at Joe SIegler's beta collection where this particular project is marked as Duke Nukem 2D.

I decided to Google for some screenshots, and eventually found this article (which is actually a part of a series about the Duke Nukem franchise), the Wiki article and this very thread. I have played the shareware version of Alien Rampage (you can get it here), which actually indicates there's a lot of potential for this engine (multi-layered parallax scrolling, different weapons for which ammo could be bought, powerups like upgradeable health, temporary near-invisibility etc., destructible objects, friendly NPCs, non-standard puzzles and so on). However, the screenshots of DNF side-scroller that had been made so far look rather bland. I understand though that this is an alpha/beta build and only the beginning of some kind of test (?) level.

Nevertheless, I'm pretty certain that if the development was completed, it would have been a great game, true to the atmosphere and spirit of the whole series. At least, Alien Rampage suggests that it was quite possible.