Yeah, they're pretty fun!
And no, they can't kill or turn your sims randomly. So no worries about that. They're pretty easy to avoid, really; just lock the door to strangers and don't even talk about them. Get some Lore skill and grab yourself some garlic to hang in your house.
I know I still love playing with them; I believe part of it is just me being attached to my vampire sims as characters.
People who only play with them strategically to get them up in higher levels and going for all the best powers and the least affecting weaknesses will more likely find them boring after a while, probably.
I just treat the power/weakness thing as another trait system. After all, vampires can be just as diverse as humans! I enjoy that.