I had much more fun playing marathon 15 years ago on a 68030 machine with a 25 MHz clock and only 8 megs of RAM. With its combination of motion, puzzle-solving, story-telling (encompassing elements like humor, irony as well as imagination), and for simply being both mentally stimulating and physically challenging... the marathon trilogy (along with its numerous 3rd-party scenarios such as EVIL, Rubicon, Tempus Irae, etc.) will never be outdone.
Never.
I would pay beaucoup bucks to get marathon running on my iPad, with these gorgeous graphics.