i have finished this difficulty , i have won the same reward of other mod , new armor , money , historic message and new game + , impossible is stupid mode , 4 shoot of plasma for cut legs ? and the plasma is for destroy asteroid lol , so wtf..
easy mode = stupid all die so fast no interet.
normal mode = monster dont die so fast , but not realy fun , bcz still so easy.
Hard = monster dont die fast , make damage , and the game become dangerous , very nice difficulty.
Impossible = very stupid monster never die , they are invincible that all , no interet , and no reward at the end.