When Duke Nukem 3D burst onto the Android Market back in November, fans of classic shoot-em-up gameplay couldn’t be happier. At least until they actually installed the game, and learned that you had to buy parts two and three separately, instantly turning a 99¢ game into a $2.99 one. Three bucks isn’t unreasonable for an Android game, but for a title that’s over fifteen years old, many users found the roundabout payment model a little sketchy. The fact that it also displayed ads (later removed) offended the sensibilities of the Android crowd, who are happy to either pay or deal with ads, but not both.

Today Duke Nukem 3D is free in the Android Market, for today and tomorrow only. That gets you the normally $1 app, but as usual, it’s only the first level (which was free in the original PC shareware version). The other two “episodes” will still cost you another dollar each. Installs have skyrocketed in the last few hours, and it is a great way to try out some classic first person shooter mechanics on your high-end Android device. That said, the app still only has a 3.1 rating; it’s probably still suffering from a flurry of angry early customers and those who are experiencing graphical and gameplay glitches in the port.

The game has caused speculation about the revenue systems behind mobile gaming. Most games on the Android Market employ one of three monetization systems: you download the game for free and deal with somewhat intrusive advertising, or you pay outright and play an ad-free game, or you download a free game with either levels or in-game perks unlockable for a fee, i.e. the “freemium” model. It looks like Machineworks Northwest wanted to reap the benefits of both the paid and freemium models, while still serving ads, at least initially. For two days the game is shifting into the fremium category. Perhaps the massive increase in downloads, and hopefully a few more dollars made on the paid extra portions of the game, will convince them to adopt a more consumer-friendly model.