Right now, yes. Several people have brought up that this game could really be played without an account (for people that just want to play one game at a time, and don't care about leaderboards in the future, etc.) so we are definitely taking into consideration developing a feature that would allow instant gameplay.
A "Play as guest" button would be really helpful!
A tip: name the game as Super Tic Tac Toe. That change can benefit you on search and rankings (because of SEO).
Guest play is a great idea! Thank you for the feedback. We did debate the name, but landed on SuperTTT because there are too many traditional and other alternative tic tac toe developers naming their applications Super Tic Tac Toe, although none of them are this game. We are however the rightful owners to supertictactoe.com which links to our superttt.com site :) Check that out too! We love feedback!