I'm currently level four Vampire, and at the stage I am now it pretty much sucks since I have to do a lot of travelling and talking due to the Main Quest...
But anyway, being a level 2+ Vampire gives you some very cool abilities and at level 4 it's pretty sick, you run VERY fast even tho wearing heavy armor, pluss you get a lot of nice attributes like a very nice spell that gives you Night Eye and Locate Humanoids in 90 sec, along with some destruction spells and a very good charm spell - only problem I've had so far is the sun and that people won't talk to you... Can't use fast travel when taking damage, as you are doing when out in the sunlight