Cons: You can't get Rested, Well-Rested, or Lover's Comfort; you may become a Daedric Prince's plaything in the afterlife
Pros: You're immune to Vampirism and between 85%-100% (people argue it) immune to all other diseases; you can kill the 'innocent' without it being tallied as a "Murder" in your stats; you can also travel
very fast.

To add a little more:
Con: During the Deadric Quest: Ill met by Moonlight, the Cursed Ring of Hircine will make you randomly transform when outside.
Pro: If you choose to help Sinding in that quest, it lifts the curse on the ring and you get an second werewolf transformation each day.
Playing as a werewolf means you need to specialize in One-Handed and Light Armor it seems.