The Dark Times: From 3D To Forever
Duke Nukem Forever was announced in 1997, but it didn't come out until 2011. So what happened in between? Surely the Duke name was not forgotten. There were a good number of other Duke Nukem games in the time between.
Duke Nukem: Time to Kill was released in 1998 for the Playstation, and had gameplay quite similar to the Tomb Raider franchise, proving that Duke can do anything he sets his mind to. The game was solid, but not as controversial or as outstanding as it's predecessor.
Duke Nukem: Zero Hour was released in 1999, but it wasn't developed by 3DRealms. Developed by Eurocom, it's a third-person shooter with similar plot elements to Time to Kill, but with a different implementation. It was also released for the Nintendo 64, giving the Duke another platform to rule over.
Duke Nukem: Land of the Babes was a year 2000 sequel to Time to Kill. Also released for the Playstation, it followed the third-person mode, and took Duke through a future where he's the only man alive, fighting the pig cops to save all the babes. An interesting bit of trivia, the game was originally titled Planet of the Babes, but the upcoming Planet of the Apes film forced them to change the title.
Duke Nukem: Manhattan Project is another genre shift, this time back to it's roots. Duke runs in a side-scrolling shooter similar to a Contra game, but played in a psuedo-3D. The environments and characters are all well-modeled in 3D, but the path taken through them is 2D. Interestingly, the company that made it was bought by another company that then went bankrupt, leaving the distribution rights for Manhattan Project in a void owned by the courts. Only recently has any resolution to the situation come up.
Duke Nukem Advance, like all games made for the Gameboy Advance, Duke just tacks the word "Advance" to the end of it and calls it a day. The game itself is a FPS similar to Duke Nukem 3D, but has an entirely original plot. It's considered one of the first good FPS games for the Advance, though that doesn't say much.
Duke Nukem: Critical Mass is next in line, if you discount completely the mobile phone games. In a genre similar to Manhattan Project, the game was released for the Nintendo DS in 2011, only a few months before Duke Nukem Forever. It's largely considered a bad game.
Duke Nukem: Forever was finally released in mid 2011, and has since been covered extensively by every game journalism site. Mediocre at best, left in development hell for 14 years, and it has very little to show for it. It's there, and it's there to stay, and hopefully the Duke name will live on past it.