I came across an article that may interest the developers and people who frequent this forum. Its 'Dslyecxi' idea of what makes a truly realistic FPS game, he is an ex-US Marine so he has experience of real combat and he also plays a lot of realistic FPS games. There are a lot of truly interesting features in here that could make a game brilliant.
Be warned though this is a very long article (22,000 words), so I’d suggest reading it over a number of days, but it is definitely worth the read.
The only thing it doesn't address is the need for classes in FPS so every grunt cannot fly a helicopter or drive a tank, but as Alliance will not feature drivable vehicles, so this omission doesn't matter too much.
http://dslyecxi.com/bestoftactical.html