Keep the 400% SP regeneration forever! We, players of Zombie Pandemic, are tired of having to stop playing the game when you're in a critical point! All of us never liked an Energy System - or anything close to it - in a game.
For the people saying that the "aim is sh*t!" or "I can't aim!", go to Settings > Controls. At the bottom, you'll see the "Mouse Sensivity" option and lower it to ~ 0.30-0.35, then press Apply and OK.