Too hectic
It's impossible to shoot the zombies and try to get any powerups or strategically shoot any barrels. It's sheer luck to get anything. Plus it doens't always register a hit, resulting in a lot of wasted bullets and zombies that take way too many hits.
Also the shotgun is worse than the machine pistol, so there's no point in using that "better" weapon.
And when the zombies get ahead of you, you've practically los, because there's no way to concentrate on the zombies behind and in front of you. So sorry, but this game just isn't very good.