The MW3 campaign was the worst-received Call of Duty campaign in recent memory. In the GameSpot review, S.E. Doster gave the single player mode a 5/10. Other reviews were similarly mixed. However, the campaign’s reception allegedly did not affect Black Ops 6’s development. In conversation with IGN, associate creative director at Raven Software John Zuk said, “…we were already pretty locked in on the story we were telling and the missions we were creating.”
Reportedly, MW3 was originally envisioned as an expansion for Modern Warfare 2. When it was upgraded to a full release, developers reportedly crunched to develop a new campaign in just a year and half (Call of Duty usually has a three-year development cycle). In contrast, Black Ops 6 has been in development for four years. According to Zuk, “The extra development time certainly gives us time to do a little bit more prototyping and a little bit more trying something out, finding out if it’s fun and if it works and throwing some things away.”
Zuk also confirmed that the campaign will be longer than 2020’s Black Ops entry Cold War, even if you were to stick to the main missions. Game length will vary depending on how much time you spend back at the game’s safe house, upgrading your weapons and chatting with your team.
Source: Gamespot Call of Duty MW3's Poor Reception Did Not Affect Black Ops 6 Campaign, Developer Says