You will be cured of all diseases. This includes vampirism. Your health and stamina will increase, as well as stamina regeneration. Your carrying capacity will increase 2000 pts as a wolf. You can use Howls, which are similar to shouts. Howls drives enemies away. You will have claws which act as both weapon and protection.
Silver harms anyone, but as a werewolf–especially in wolf form–silver hurts you even more than before. You will not receive any resting bonuses. Racial abilities will not carry over. You cannot use equipment, magic, or other powers. If NPC’S witness your transformation, they will run, or attack you. In the least case they will treat you like an outsider, saying “I find your wolfish grin. . . unsettling. " “You smell like a wet dog. " “Is that. . . Hair growing out of your ears?” and even “Ah, you’ve been playing with your hounds again?” But Eorlund Gray-Mane will defend you if you transform in the middle of Whiterun.