Two major gripes: #1 dump the money magnet. Too annoying, it takes way too long to scoop up the cash. Also, it's a reall drag to miss money on the ground after you destroy the whole city. Again it's because of the money magnet effect.
Please get rid of the Money sponge" effect, where you have to wait till the coins are 'absorbed" by your magnet. Just give us the cash for each kill, and make the game a little bit harder, longer.
Annoyingly difficult to understand weapon selection and unlocking system. Make it more intuitive, or have more help info.
Lag, lag lag.
Fun game but for the two points.