The hammer is a one hit death melee weapon, but has a three second interval in between hits making it the slowest weapon in the game. You run very slowly with it.
The sledgehammer is the most powerful weapon in the game so take advantage of this and be wary of it's greatest weakness: speed. After you attack, there is the three second cool-down before you can attack. So, properly strategy is needed. Often, camping is a good idea with this weapon (it is actually the best camper).