Do not even attempt to watch this video unless you are a Renegade freak. Only then you’ll notice the subtle changes in the gameplay along levels.
Having scored 0,5 million I have asked what is needed to get 1 million. Well, 72 levels are needed.
I am not pro enough to get there with one game. That required retaking some levels. However, this game may work as a Turing test. Anyone reaching that far with a normal gameplay, is definitely not human :)
Some interesting observations:
1. Difficulty increase varies on advanced levels. In short, with each round (5 levels), the enemies are stronger and act quicker. However this does not matter as much on level 1 and 2 (subway and harbor), because you throw them down anyway. On level 4, you have 135 seconds to take out 4 guys, and the remaining time may be used to take out the boss in level 5 (possible in about 30 seconds with some luck).
2. Far in the game, the most difficult level becomes 3, where you have 135 seconds to take out at leas