If only this add-on couldn't be finished in a single day...
Why am I saying this? Because there're some ridiculously huge map packs around for Duke Nukem 3D, but the great majority of these levels is poorly designed and you'll probably stop playing after an hour or so. For example, Duke!Zone features more than 500 fan-made maps; to be honest, that's perfectly fine because Duke Assault has over 1500 custom levels. Understand that we're talking about 500 plus 500 plus 500 maps! The problem is that they're almost all quite unbalanced and not fun at all, so this massive number can be reduced to only a dozen well-crafted levels.
The purpose with Duke It Out In D.C. is to bring only those gems that will really feature some good action sequences and satisfy the player. In this add-on, Sunstorm wants you to control the American hero, Duke Nukem, in order to save Bill Clinton from the aliens. Since there is a simple background story, the maps in this expansion are played in a logical order, starting at the White House and getting through the Smithsonian museum, the Washington Monument and some other known places of Washington, D.C.
There are ten levels in this add-on and that's it. Sunstorm did draw a few themed textures and sprites, but there aren't new enemies, sound effects, music or weapons. The content of Duke It Out In D.C. is very thin, and there is literally nothing else to do here after finishing the new campaign. At least the levels are cool and more hardcore-focused than the original maps from Duke Nukem 3D. You start the game with little ammo and a few basic weapons, yet you have to kill a lot of enemies simultaneously. This may sound punishing for newcomers, however Duke veterans will find this particularly captivating.
The campaign to save Bill Clinton is pretty short, though. It's true that you'll spend some extra time killing the relatively large amount of enemies per map and searching for keys, switches and secret passages; however all this stuff can be done in a single day at the hardest difficulty level without too much trouble. But I'm happy already to play some great levels that Sunstorm carefully crafted with lots of attention to detail.
Actually, the only real problem you'll have with Duke It Out In D.C. is to install and run it on modern PCs. The well-known programs to run MS-DOS games, such as DOSBox and VDMSound, won't do the job, as far as I'm concerned. I had to spend some hours of my free time to understand how I should proceed to run the expansion along with the Win32 ports (personally I used JFDuke3D), which consisted in unpacking the original Sunstorm files and re-creating them with a common file extension. It wasn't a walk in the park, as you may already noticed.
Installation issues and derivative content aside, Duke It Out In D.C. is a must-have expansion for die-hard fans. If you don't want to wait for Duke Nukem Forever anymore yet your old-schooler blood needs some extra "Nuking", then the campaign to rescue Clinton is a good reason to incorporate Duke once more and do some nice alien butchering sessions.