The first thing you notice when you visit Michelangelo's Pieta in St. Peter's Basilica is the thick bullet proof acrylic glass that surrounds it. The reason behind this is that sometime in 1972 a man named Laszlo Toth tried to destroy the sculpture with a hammer. After painstaking restoration, the statue was returned and the bullet proof glass installed.
Now back to the artwork, the statue is of course not proportional. The figure of Mary is exaggerated in size by her flowing robes and Christ's body is smaller than that of a full size adult. The statue is also pyramidal in shape and the vertex coincides with Mary's forehead. Some more things you may not notice, first look at Christ's face and body, notice that not all the wounds are there. Another is Mary's face, she seems much younger for a woman her age would appear. Surprisingly though, the Pieta appears to be very natural in size and proportion.
If you want to visit the Pieta but find Rome to be a long commute, there's an authorized replica in the Manila Cathedral. Look left when you enter through the front gate.