One of the more rational theories suggested the surprise was in some way related to the overdue Half-Life 2: Episode 3. We hate to be the bearer of bad news, but it just isn't so. When the guys over at Halflife2.net asked the company whether the surprise was Episode 3, Valve boss Gabe Newell succinctly replied, "it isn't Ep 3."
Newell also put another rumor to bed in another email. A supposed Half-Life teaser image began circulating after Valve announced the surprise, but Newell acknowledged this as a fake, thus leaving gamers to stew in their own thoughts until June 14. So, if the big secret isn't HL2: E3, then what is it?