Many people come to Puerto Rico for a short period of time  (taking a cruise somewhere else or business. )  So when you asked what they did, they pretty much say went to El Morro and Old San Juan.  If you are one of those, Isla Verde will offer you a chance to see a fair beach to enjoy at 15-20 minutes from most of San Juan's hotels.  

On the west end you'll see more hotel/urban settings.  As you drive along the coast towards the eastern end you'll reach the Balneario de Isla Verde (the public beach)  Now keep driving a bit more and you'll see more beautiful shore, a bit more wild but really nice. Some places have more waves, but there's also a few coral reef with places for the younger kids to play.

Isla Verde is not the best beach in Puerto Rico, but it's like a convenience store. Great location, parking close to the shore and It has enough for you to say: you went to the beach and had a good time.