Amazing Game!
This is a great game! It is slightly long but i was easily able to beat it in one sitting.
The easiest way to survive is to fully upgrade ur first gun. Then aim for gettin the final and best manual gun. After you fully upgrade that try to get the $1000 gun (splitter or somethin its called). after That is fully upgraded, get another fully upgraded gun 8. always remember to upgrade armor and hp along the way.
if you do everything right, the last level should take you less than a minute.
Once again great game! It could use a free mode though or survival