Those virtues would suffice, but Puerto Plata succeeds because of its history and close proximity to a bevy of other activities. From here you can get a lesson on the past at the Fort of San Felipe (one of the first strongholds in the Americas, it looks like a little like an old European castle, moat included) or tour the a rum distillery (Brugal Rum makes its home here) just as easily as you can sit on the beach and make a cocktail.
The city of San Felipe de Puerto Plata was founded in 1503, but its main attraction is significantly more ancient: Take the only aerial tramway in the Caribbean and ascend the the cloud-enshrouded, 793-foot Mount Isabel de Torres for stunning vistas and the lush botanical garden at the peak. Then cool off at the Ocean World Adventure Park, a Sea World-type theme park where you can purchase "encounters" with sharks, sea lions, and dolphins for a fee (around $70 and up).
While the city of Puerto Plata has seen its fortunes rise and fall –- initially a vitally important port, later destroyed to prevent British piracy -– the specimens at the Amber Museum stay preserved. This Victorian-style mansion in the heart of Parque Central downtown contains rooms of ancient, Jurassic Park-like creatures, preserved for the ages in fossilized golden sap. Is that a weird attraction? Yes, but there's not much like it, and that makes it special.