I used to abandoned this game, but I decided to change my mind after watching the 1CC run on maximum difficulty for a little bit. Looks like it's [very] possible to 100% though not easy.
Technically I didn't earn all of the achievements. However, the two achievements related to golden guns collection did not work in XXL. As a result, I had to start playing the original version from scratch. I'm not sure about the challenge levels though, as I have not tested. I've beaten the game and earned 100% on Xbox 360 version back in the day.
