The free, iOS version of Marathon that Bungie mentioned last week is now available in the App Store. The base application itself is free, but there are in-game purchases that improve the experience (better textures) or provide cheats (“Master Chief” mode).

I’ve not played a lot of games on the iPad, but due to its origins, this may be one of the more difficult ones to control. There’s an on-screen joystick for handling movement forwards and backwards as well as strafing side-to-side. Aiming and turning are controlled just by pressing on the screen where you want to aim. Primary fire has an on-screen button, but there’s an option to do it by tapping the screen. There’s another on-screen button for secondary fire, and one for the use key, and hitting the motion tracker switches to the map screen. There are also two more buttons to scroll forward and back through the available weapons. And a pause button. Marathon’s movement speed is a lot faster than Halo’s, so moving around the game’s labyrinthine levels proficiently with the touch controls takes a bit of work.

It’s hard for me to see this as much more than a novelty– hey, look, I’ve got Marathon on my iPad! Playing seems less enjoyable than other old game ports to the platform, like the Monkey Island adventure games, and just like those games, there are a lot of options– Aleph One, which served as the basis for this conversion, runs all the Marathon games on all modern operating systems, plus Marathon 2 was ported to XBLA, so if this game is serving people who have no other way to play Marathon, it’s because they don’t have a Mac, a PC, or an Xbox. Perhaps the target audience is PlayStation owners who don’t have a computer, but own an iPad? I’m not sure.

I’m guessing the main game is free in order to maintain compliance with Aleph One’s license, although if history is any lesson, it might only take one developer who has contributed to Aleph One and alleges that Apple’s App Store license is incompatible with the GPL to get the app removed. Of course, it’s also undoubtedly true that this project took a considerable amount of effort, for which the seller would like to be compensated; hence the in-game purchases of high definition upgrades and cheat codes. I find it hard to imagine how many people will want or need those– the game looks plenty good to me in its current form, and I haven’t seen screenshots of the paid upgrade. I can see people having enough difficulty with the game to want the cheat code, but there’s already a wide range of difficulty levels, and myself I wouldn’t really feel good about buying a cheat code– perhaps others won’t have that problem.

The iPad conversion seems to score over the other recent port of the Marathon franchise in one important area: unlike Marathon 2 on XBLA (and the more recent port of American McGee’s Alice) it doesn’t give me motion sickness.