Downsides: turning or re-turning in front of people grants a 1000 gold bounty. Slow health recharge rate. Feeding only works on humanoids.
Now vampires, they get bonuses, but they get EQUAL penalties to something else. Frost resistance, Fire penalty. All equal. At stage 4 you get the invisibility spell but you will NEED that just to go back to stage 1 where you can walk in towns again. But, a vampire has no pure bonus, everything it has positive it also has negative on something else.
So, I don't really see why anyone would go vampire over being a werewolf...
Please, correct me here.