Becoming a vampire does give you some advantages but they certainly don't seem to make up the disadvantages. I could see if you were more powerful at night and weaker in the day but in its current form it seems like more of a pain than an additional power.

advantages
-extra frost resistance
-immune to poison and disease
-illusion spells and sneak are 25% more effective
-some decent powers as you transform further into a vampire but really anything you couldn't really get from some higher level magic spells.

disadvantages
-in the day you get no health, magicka or stamina rejuvination, yet you don't seem to get faster regen at night for any of those either.
-people comment on your pale skin and hungry look in your eyes and thats cool, but at level 4 everyone attacks you. So how are you supposed to sneak and feed on someone in a house if every guard in the city is trying to kill you for just showing up?
-feeding makes you a weaker vampire not a stronger one. Doesn't that seem a bit backwards to anyone else?