The hype for Battlefield 1 has been electrifying since its debut in May of this year. It's only natural that its beta would be popular. Even then, nobody expected 13.2 million players to have participated.
With 13.2 million participants Battlefield 1's beta has become the most popular of its kind in gaming history. The sheer number of gamers who have tried the game has prompted widespread discussion of its quality, of which the overwhelming majority has been positive. The most notable positives have been oriented toward the game's graphical quality, fun factor, and vehicle diversity. Negatives point toward sniper imbalance, map size being an issue at times, and horse design being finicky.
EA has released an infographic regarding the Battlefield 1 beta which includes statistics related to class popularity as well as additional milestones. You can view it below.