Even though it failed to meet initial sales expectations, Tomb Raider has now reached 8.5 million sold, making it the highest selling game in the franchise. This does include copies of the Definitive Edition on the Xbox One and PS4, as well as, of course, PC versions sold. This is good news; Tomb Raider was an excellent game according to Gaming Nexus' Cyril Lachel, and I agree.
Hopefully this sales landmark will encourage Square Enix to keep the quality so high in the upcoming sequel, Rise of the Tomb Raider, which is due out this fall. However, Rise of the Tomb Raider will be released only on the Xbox 360 and Xbox One, as a result of an exclusivity agreement with Microsoft, so it's unlikely that it will sell as many as the first, which was also available on other platforms.