Ugly Americans: Apocalypsegeddon

As the description states, finish with any of the four characters. There are 11 cases (levels) to go through. For me Case 5 was rough because of the fast tough enemies in later part of that level. What worked for me was to keep moving, preferrably in circles, to avoid enemy attacks and the fast enemies chasing you. If your still having trouble beating that level, go back to earlier levels and level up some more. That helped me a great deal. The later cases get tougher from that point on, so it's a good idea to level up. Once you get to around level 20-30's, you should be able to beat most if not all of the levels. The max level is 60. If you still can't beat all the cases, then try playing online or with a friend. The extra firepower helps here too.
Good luck!