Once the game is finished once the player enters the challenge mode which is to loop 6 levels in the shortest time.
This game mode has a huge lifespan as the scope for growth is important, on my first run on level 1
I slammed a 12m30s and after "a little" practice I came to 4m22s.
Note the challenge 4 and 6 are much harder than others, and especially 6 will require a lot of practice before you see the end as it is long and trying nervously.
In conclusion, the average player will play in a dynamic shooter, but much too short, for hard against player
will spend a hundred hours (in my case) on the challenge mode to optimize its time, given the prevailing price today
it makes an excellent price / fun.