Bethesda said Fallout 4 "launched with approximately 12 million units worldwide to meet day one demand, representing sales in excess of $750 million." To be clear, that's not the same as launch-day sales which, while no doubt astronomical, haven't been released yet. Bethesda did say, however, that the Fallout 4 Pip-Boy Edition was "the fastest-selling collector’s edition of any game in history at leading retailers," and that some stores were reporting better day-one sales for Fallout 4 than for any other game this year.
"A huge thanks to our fans that’ve made this all possible,” Fallout 4 Game Director Todd Howard said. "After four years of development, it's not complete until our fans get to play it and make it their own. We can't wait to hear about their adventures."
Bethesda also noted, as did we, that Fallout 4 was at one point the number-one game on Steam, with more than 470,000 concurrent players at its peak—a record-setting number, and enough to briefly push it past perennial dominators Counter-Strike: Global Offensive and Dota 2.
Determining precisely where a game stands relative to its competitors is a tricky business, as publishers tend to make the most noise about whatever number leaves the best impression—sell-in, sell-through, preorders, and all that sort of bafflegab. But "successful?" Yeah, I'd say that's probably a fair assessment.