I never play those levels in Single Player, Flash, I prefer playing them online in a full server when you can actually compete with others to see who finishes the quest first.

My former best friend was addicted to this game and thought I should give it a try, so he installed it at my PC. The first time I tried it by myself (that evening) was on-line, and I've never bothered to to try Single Player since 2D shooters games generally aren't really my kind of game, but on-line it seemed to be alright. So I stayed.
And for Single Player gaming I just prefer consoles by far..