In my opinion, their greatest achievement has been in its educational system. Despite its huge list of problems, UPR enables people of any background to receive an affordable high quality college education. In the US, you're basically forced to take out huge loans that might take decades to pay off. This should mean you'll get access to lots of highly educated individuals, although I don't know if that's the case in practice.
One of my biggest complaints is its poor representation in the US government. If you're living in Puerto Rico you can't vote in any of the US's elections, even though the actions of the president and congress could potentially affect you. e.g. You could get drafted and sent off to war.
Puerto Rico has its own constitution [0], which arguably grants stronger rights to its citizens than the US constitution. For example, wire-tapping is explicitly illegal. It also includes entries allowing employees to organize into associations and collectively negotiate with their employers, as well as go on strike.
An interesting point is that everyone is required to get a voter ID in order to participate in an election. This isn't seen as a problem, and getting one is incredibly easy. I found it incredibly surprising this wasn't the case in the US.
Food is amazing, but there's very little variety. Since there's so few people from different cultural backgrounds, you mostly get the same templates repeated everywhere. In the last decade it has been slowly improving. If you're a vegan or vegetarian, or if you require a gluten-free diet (i.e. coeliac disease), you'll have a hard time eating out.
Due to cabotage laws, you can't import directly to Puerto Rico. Everything has to go through a US port, which translates to increased costs.
Shipping stuff to Puerto Rico is usually more expensive than shipping stuff to the contiguous United States. I'd guess it's comparable to Hawaii.
Even though both English and Spanish are considered official languages, you'll have a very hard time living there if you don't know Spanish.
[0] https://en.wikipedia.org/wiki/Constitution_of_Puerto_Rico