Although he's not quite as well presented as his counterpart due to the inability to access future technology that makes you look all shiny and new, there's no better choice for the Illusive Man than Martin Sheen. Physically he fits the part quite nicely (and can be touched up by the magic of Hollywood), but the single most important thing he's got going for him at this point is he actually was the Illusive Man in the series. You can't get more perfect than having the actual dude who voiced this famous character playing him, can you? Since the Illusive Man is such an integral part of the Mass Effect series, the role should go to an established actor who knows what they're doing. Given that he's played the character for two games and lived through all the experience, you can't get better than having Martin Sheen. He's also an established actor already, most recently popping up as Uncle Ben in the Amazing Spiderman. Who doesn't want to see Martin Sheen standing in front of that lovely dying star backdrop and eventually descending into bonkers indoctrination?
Dan Curtis is approximately one-half videogame knowledge, and the other half inexplicable Geordie accent. He's also one quarter of the Factory Sealed Retro Gaming podcast.