As beaches go, it's OK. It's not as wide as you would think, certainly not compared to the beaches in Southern California or the East Coast of the United States, and when I was there, the beach was very crowded. The water was also cooler than I anticipated. There's a boardwalk that extends along the beach until the resorts take over, there's a decent pier, and there's a partial breakwater that makes the water in one area as smooth as glass and very safe for young children. Further out in the ocean, there's surfers and a few sailboats. Since the area is a tourist magnet, it's expensive to rent umbrellas and chairs and the like. Overall, as long as you can afford it, the vibe is quite good. I liked the fact that there are visitors from everywhere - the continental US, Europe, and from places like Japan and Korea as well. The people watching is fantastic - walk along the Boardwalk toward Diamond Head and you'll see more locals - beautiful girls walking or jogging or heading out with young guys for the day's surfing. I'm not sure what these people do for jobs or to make money, but that's really not the point of Waikiki.
I also enjoyed watching the sun set into the Pacific; it draws a crowd, and it was a nice treat.