First, the Good
As a product, D&D Beyond is slick. The interface is reasonably easy to pick up (the search features could use some minor improvements for usability, but that's mostly nit-picking). All in all, it’s a well polished reference engine.
All of the content from the SRD and adventure supplement PDFs (as published on the Wizards.com web site) are also included for free. For instance, Snilloc’s Snowball Swarm and other spells from the Princes of the Apocalypse player PDF is included in the free tier. As a player, you also get 6 unlocked character slots for free.