Puerto Rico has a good economy, and it would make a good addition as the fifty-first state. The hurdle standing in the way of statehood is not the island's economy, but the unwillingness of its people to identify as American. Puerto Ricans are happy being a territory because they do not want to be a state.
The only issues holding up Puerto Rican statehood are political. The first roadblock was the support of the Puerto Rican people themselves. This roadblock was cleared in 2012 when the people of Puerto Rico voted in favor of statehood for the first time in 114 years.
The second roadblock is approval by Congress. This is difficult because it would change the balance of power in Congress by adding 1 Representative and 2 Senators who would all almost certainly be Democrats for the foreseeable future. It is, obviously, difficult to convince Republicans that this is a good idea. These political considerations are the reason Puerto Rican statehood is not a slam dunk decision.