(feel free to respond with other good things or bad things about them...)
Rarely making appearances, they have still managed to kill two (possibly three) Doctor's. Their leader once regenerated as Timothy Dalton (the actor who turned Bond away from camp)! They are insanely varied in weapons and capabilities. They all have understandable motivations. They are the absolute perfect mirror for the Doctor, as seen when he faced the Dream Lord.
The best part about a Doctor Who villain is the scare factor. I spent many nights hiding behind the sofa from Daleks, Weeping Angels, Vashta Nerada etc. Time Lords are only people who look like humans, with nothing scary about them minus a slightly creepy hand that can disintegrate people. NOWHERE near the quantam lock of the Angels or the classic EXTERMINATE of the Daleks
The weeping angels are great villains because they are unique and, like you said, not overused. They are bone-chilling and hair-raising. The scared me half to death and have their own ability. An ability I've never seen before: the ability to send you back in time and make you live out your death. Brilliant! It's like everything you ever knew and loved died out and you have to start over.