There wasn't that much difficulty in the game, but it's still good. It's mostly because everything is done really nicely with detail. It's so much fun to get new weapons and achievements and stuff. I guess the true challenge was the time limit. It reminds me of a game Tom Fulp made when Harold Camping said the world would end in 2011. And it's 2015 now!
Don't worry, nothing bad really happened because people believed in it. How could it? The sound effects were great. It was fun to see these iconic buildings in one spot. It was even more to take them down!