First and foremost, too much lag. I dun wanna empty my magazine only to watch the bullets be counted whenever they feel like it. Reload takes absolutely forever even with upgrades, weapon dmg and accuracy are no better even with upgrades, you dun earn jack shit for money, and they come so frequently with such horrid controls (due to more lag) that I can't even open the shop to heal before I've basically become a lost cause while waiting for the shop to open and for my shots to actually fire.
So unless you hit an enemy from the side, you need to hit them completely head on with your shots. I actually managed to complete an entire level while I rated and typed this comment without even looking, so what does that tell you about the game? Go ahead and downvote cuz you don't wanna see someone saying unkind things about your favorite game...but sometimes you need to hear the ugly if you wanna make something good.