Great UX, great documentation, smart (if limited) integrations, a lot of power lurking beneath the turn-key products.
The commerce product is still baking. Shopify is better at bulk inventory management, payment processing, shipping, and fulfillment.
While Squarespace positions itself as a consumer/DIY product, the benefits the platform offers as a white-label SMB product are already powerful and evolving consistently. The Circle program lights a path to a thriving development community that can guide future iterations of the platform.
Squarespace lets me deliver SMB clients a sophisticated, data-driven content strategy without the expense of a from-scratch agency website or the poor quality of the DIY, my-niece-has-a-friend-at-college-who-does-websites product. While turn-key Squarespace sites ensure that I can provide an attractive, reliable, basic website to my clients, the real power comes in the integrations (MailChimp, Acuity, OpenTable, etc), easy CSS injections, and the deceptively powerful collections functionality (blogs, galleries, calendars, and summaries). Brass tacks: I feel confident that I can sell a Squarespace site, including content strategy and monthly marketing retainer, against agencies charging 2X or 3X for similar white-label or custom-built products to SMBs.