The human capital of id was valuable, but I think you are underselling their brands and technology. 150 million for the ownership of some of the most iconic brands (Doom, Quake, Wolfenstein) in FPS gaming doesn't seem that expensive, especially considering that it's much easier to sell many copies of a game in a well known franchise than to to sell games in a new franchise. The latest Doom sold over a million copies, Wolfenstein; The New Order sold over a million copies, the latest "Quake" (Enemy Territory: QUAKE Wars) probably sold over a million copies as well.

In terms of human capital, Carmack is one of the most respected technologists in gaming, but I'm sure ZeniMax didn't expect him to stay with them for a very long period. At the time id was bought by ZeniMax it seemed like Carmack was spending a lot of time on Armadillo Aerospace too.

In terms of tech it seems id wasn't the leader it used to be anymore (their early engines were used by Half-Life and CoD), taking into consideration Unreal Engine 3, Crytek Engine (being used for Bethesda's own Prey, the previous installment running on idTech) and Unity.

On the other side, Activision bought Infinity Ward (developer of Call of Duty) for just 5 million [1]...

http://venturebeat.com/2010/03/04/lawsuit-details-activision...

I think you're right, but the Doom name has a lot of marketing value.

I'm inclined to agree, but having played Doom 2016, its clear the creative and technical mindshare is still intact. Especially since the other ZeniMax companies are (more than likely) going to use that same technology.