Duke Nukem 3D is already available to play on the App Store now, and just in time for the sequel's 20th anniversary, Duke Nukem 2 is coming to the App Store soon. Interceptor Entertainment (the folks behind the recent Rise of the Triad reboot announcement) has teamed up with 3D Realms to bring the second, side-scrolling Duke Nukem to iOS, as you can see in the reveal trailer, up now. They're working on a version that will contain all of the original's 32 levels, plus some new artwork and music, as well as touchscreen support (of course), and leaderboards.
Interceptor says the game is due out on iOS in April for a price of US$1.99. We'll look for it then.