We had the pleasure of staying right on lanikai beach for the month of August (see my photos looking towards the moks and looking south). As per previous reviews, the beach does get noticeably busy despite the fact that a pretty much identical (and much larger) beach (Kailua beach) lies just around the corner - Kailua includes facilities such as bathrooms and showers... Lanikai beach does not include any facilities - so beware of this before venturing out! We were lucky enough to have stayed in a home directly on the beach, so we had access to showers and bathrooms (and trust me - showers are a must after this beach.... The sand is like powder and just coats wet skin). The snorkeling at lanikai is excellent when the tide is going out and the water is clear - the snorkeling is best towards the north end of the beach and out about 50 yards (crystal clear water). We saw hundreds of fish, and turtles daily! If you want the best snorkeling though, try sharks cove in the north shore!
Other fun activities include kayaking out to the moks (takes about 15-20 minutes), hiking/ running the pillbox trail - a great morning/ early evening run with amazing views, and of course, drinks at buzz's steakhouse (order the bfrd)!!
All in all, lanikai is an amazing beach if you are looking for soft powdery white/gold sand, calm waves, coconut trees, and blue water! Best beach on Oahu for small children!!! Definitely my favorite beach!!
If you are looking for a quieter beach scene, with swaying coconut trees, equally clear blue water and white/golden sand (slightly coarser) try the north shore. The beach at chungs reef (in the north shore) also has excellent snorkeling, crystal clear water, and white/gold sand - and is right near secret turtle beach and sharks cove.