Don't be affraid... It's for fun.
For those afraid by the clock/timed mission/healing daughter bucket, be safe and believe me it's not a big deal. I finished the game with S rating first time and I'm not such a good player. Anyway this is the kind of game you finish once and comeback later because it's quite hard to do every task in one run. Even if you keep failing you'll always have the chance to start over with your leveled up character.
Otherwise just enjoy zombie killing, extreme gore, crazy/stupid situations and look for amazing custom weapons.