We absolutely loved Ka'anapali Beach. I think it's perfect. Where else can you swim with a green sea turtle in nature, run into a Hawaiian monk seal sunbathing in the wild, and eat delicious Hawaiian rainbow soft serve, all within walking distance of each other?
Some may find this beach too touristy, which is true, but there are some parts of this beach which felt relatively desolate and private to us - that stretch was in front of the resort we were staying at, Marriott's Maui Ocean Club: https://www.yelp.com/biz/marriotts-maui-ocean-club-molokai-maui-and-lanai-towers-lahaina-maui. Most of our days on Ka'anapali Beach were spent in front of or near the Marriott.
We did venture up to Black Rock Beach one afternoon for snorkeling. From the Marriott, it was roughly a one-mile walk up the Ka'anapali Beachwalk. We enjoyed our time snorkeling at Black Rock, but in general, Black Rock was too crowded (and too far) for us to spend our general beach time there. To read more about Black Rock Beach, visit Black Rock Beach's Yelp page here: https://www.yelp.com/biz/black-rock-beach-lahaina.
We had more fun snorkeling off the coast in front of the Marriott because there were hardly any other people around, especially in the water. The beach was thinner, more coral showed up almost immediately when we swam out, and the ocean doesn't get as deep as quickly as it does out at Black Rock (safer). One of the most memorable experiences for my wife and I was swimming with a green sea turtle here. It was just so cool to float, hang out with, and watch it graze under water. The turtles are known as "honu" in Hawaiian.
The water is perfect. The sand is perfect. The sea creatures are perfect. The vegetation is perfect. The view is perfect. If looking out to sea from the beach, you can see the island of Lanai to the left and Moloka'i to the right.
The waves aren't big here. At least, they weren't during our visit. However, we saw plenty of surf instruction as well as kayaking, paddleboarding, parasailing, and other water and beach activities. With so many resorts and condos lining Ka'anapali Beach, it's only natural for it to have all these businesses with things to do. Our family brought our own sets of snorkel gear. I also rented a set for a day from Aqualani Beach & Ocean Recreation: https://www.yelp.com/biz/aqualani-beach-and-ocean-recreation-kihei. They have a small building in front of the Marriott. My snorkel gear cost just under $30 for a day.
I've read that the beach, which largely runs north to south, goes for about three miles. While resorts and condos do line most of the beach, the island of Maui (or whoever's in charge), has done a great job of keeping the beach pristine and classy. Besides the resorts and some small huts like Aqualani's, Ka'anapali Beach is clean and safe with no other vendors except for Whalers Village, I think. What I'm trying to say is it's not filled with a bunch of shops like Front Street in Lahaina or has a tacky boardwalk or anything like that (e.g. Venice Beach), even though it's commercialized.
Whalers Village, which is situated just north of Ka'anapali Beach's midpoint, is a large outdoor shopping mall, with restaurants like Leilani's and Hula Grill, on the beach: https://www.yelp.com/biz/whalers-village-lahaina. Hula Grill has its popular Barefoot Bar. Whalers Village has been around since 1970. The highest-end store tenant there is Louis Vuitton, but there are plenty of "everyday" stores too. If you forgot or lost something like sunscreen or sunglasses, or just want some quick snacks and refreshments, there's an ABC Store (convenience store) at Whalers Village.
I recommend walking the Ka'anapali Beachwalk. It's a nice, paved path that runs parallel to the beach. It covers most of the beach. The walk is scenic and pleasant.
Along with walking the Beachwalk, snorkeling (lots of colorful and beautiful fish to see), and swimming with a sea turtle, another highlight from our time at Ka'anapali Beach was seeing a Hawaiian monk seal relaxing and sunbathing on the sand in front of the Marriott: https://www.yelp.com/biz_photos/kaanapali-beach-lahaina?select_video=B5vO_cZf7UkK4RpOA0l_Tg. Neat!
Check out Beach Walk Kau Kau To Go and treat yourself to some delicious soft serve in a cone. I recommend the Rainbow with blue Hawaii coconut, mango, and strawberry swirled together: https://www.yelp.com/biz/beach-walk-kau-kau-to-go-lahaina-2. There's a Starbucks next door too.
Finally, if it works with your schedule, try to visit Ka'anapali Beach during sunset. There are some pretty awesome sunset views here since you're on the west side of the island. read more