buggy
It lose fun because it simply gets EASIER as you past levels...
I stopped at lvl 42 cause all levels are the same with 5 more zombies after a while, i mean, they dont even come faster or with more HP around lvl 20+
And as people said, get 3 atk rate and everything else in shells and just wait on a corner killing everything with no problem if you want those 100 trillion scores...