I went with my parents when I was in high school. We stayed at a resort in Ixtapa (which is one city over) but visited Zihuatenejo a few times to go out to eat. Quaint town. Both places are beautiful. Definitely worth checking out.
Ditto on the other poster... stayed in Ixtapa, went to Zihuat. Nice little fishing village... enjoyed grabbing a bite of lunch outside, next to the bay.
Honeymooned there 10 years ago. Stayed at La Casa Que Canta. Awesome! If going, look there or Villa Del Sol.
Stayed at Villa del Sol two years ago. Wonderful place, amazing restaurant. "Leading Small Hotels of the World" place, and earned it, IMHO. Town is quaint in that ain't nothin happenin way. A brew, a bite, etc.