Friends... I believe I may have found a solution to our gamepad problem. It seems the game will only detect an Xbox360 controller (I'm just assuming this, since I don't own a 360 controller to test this out with).
Anyways I am having the same problem as you all. I am using one of those Playstation 2-to-USB adapters to try to play the game, but the game is only letting me use the mouse+keyboard combo. I then tried using my PS3 Sixaxis as well as Dual Shock 3(using the lib-usb method; google it) but that didn't work either. Lastly, I thought to myself, "Hmmm, I wonder if there is such a thing as an Xbox 360 Controller Emulator." Lo and behold, there is!
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If the link wont show, just google "pc emulate 360 controller" and it's the second link.
This method requires some extra configuring in order to map the actual buttons (the Sixaxis buttons come out reallyyyyy screwy, but the PS2 controller almost maps out perfectly by default). Anyways, as of right now (11:13PM Eastern Time) I was able to get the game to at least recognize my Sixaxis (as well as the PS2-to-USB adapter). The analog sticks work perfect, but like I said all the other buttons are screwy (you have to edit the INI file somehow). I'm about to go to bed however, so if anyone can actually figure out how to remap the buttons, please reply to this post so that I(and many others) wont have to figure it out tomorrow. Goodnight, fellow gamers!
P.S. Awesome game, Activision!!