What Key West beaches do well
Fort Zachary Taylor Historic State Park combines swimming, snorkeling, shade, picnicking, and a major historic fort. Florida State Parks calls it Key West's favorite beach and recommends water shoes. Other public and resort beaches can provide sun, water views, and convenient swimming, depending on conditions.
What beach-focused travelers may miss
Key West does not offer the uninterrupted broad sand associated with many Gulf Coast, Atlantic Coast, or Caribbean resort destinations. Shorelines can be compact, rocky, or affected by seagrass and changing water conditions. A traveler who judges the destination by the quality of its beaches will be disappointed, not merely surprised.
The stronger reason to come is the marine environment
The Florida Keys National Marine Sanctuary surrounds the island with coral reefs, seagrass, mangroves, sand flats, shipwrecks, and wildlife habitat. Many of the most memorable water experiences require a boat, kayak, snorkel excursion, or fishing trip rather than a beach chair.