Play without an account: the tutorial starts at once, then you play the computer as a guest. Your guest wins move to your account later.
Other changes
New visitors land directly in the tutorial instead of the sign-in screen. After the tutorial you pick a starter deck and play against the computer, no form needed.
As a guest, your wins and the starter decks you have beaten are kept on your device. When you create an account, they count for the deck quests, XP and Silver (once per new account).
An account is only needed where it matters: online games, quests and rewards, collection and card packs, shop, trading and invites.
Already have an account? Log in from the main menu (top right) or from the first tutorial page.