To get Expert I believe you need to send every wave before the counter reaches 175. Game speed does not seem to effect the score so keep it on x1 if your having trouble getting them out that fast.
For all the people complaining about missing, you need to train your combat skills in school first before you go adventuring, then you wont miss anymore.
Is there a way to un-equip your gun? I played thru a level and only used my shoulder weapon but didn't get the badge. Not sure what I am doing wrong there.
CounterTerrorist complains he only gets 2% xp per fight and only has 41 energy so no way he can level but that is 82% level base, however when you add in free energy from mushrooms and wishing wells plus the fact that you can not use all 41 energy in the 3 minutes it takes to refill an energy you should still be able to level with no down time.
Every time you level your energy refills. Unless you suck you should be able to level off your energy and so have no downtime. Also when you get badges your max energy raises. You can also buy potions to give energy. I am level 17 and haven't had to wait once for energy yet.
Well another lame thing. I got to Survival mode than had to go. When they say you can't Save not only can you not save while playing but if you leave the game it resets you all the back to Normal.