Art is subjective but I think good street art should be transgressive, make a statement or speak to the community that it is painted in. Most of these represent the later by showing the people and the culture in the state of Quintana Roo, where Tulum is located or Mexico itself in the case of the skeleton.
Tulum has a plethora of street art with many simple concrete walls begging to be illustrated on and many visitors from around the world eager to paint.
I realized while walking around photographing the street art in Tulum–that many of the places that I have visited that have excellent street art also have intense gentrification. Street Art tends to follow the emergence of hip or maybe its the other way around.
In spite of the fact that Tulum is a town taken over by tourism–it is a magical place to visit.