Given the most vocal opposition to the deal has come from Sony, the makers of Playstation it can hardly be seen as an "independent lawsuit" as appears to be being touted by the tech press. There are also some other oddities about the case. 

For example, it is not a class action lawsuit and it names only Microsoft as the defendant in the case, not Activision Blizzard.

The 45-page document argues that if the acquisition is allowed to proceed, it would have a lot of negative effects on "the industry" as a whole. These include reduced competition, higher prices, less creativity, decreased output, and Activision games being locked to Microsoft's own platforms.

Apparently, the proposed acquisition poses a substantial threat to these ten play station players and to the public at large... and may cause loss to the Plaintiffs in the form of higher prices, less innovation, less creativity, less consumer choice, decreased output, and other potential anticompetitive effects, which deprive the Plaintiffs, and the public at large, of the salutary benefits of competition.

"The proposed acquisition of Activision Blizzard by Microsoft may substantially reduce competition in the labour market for video game labour talent," he complaint claims.

"Employees in the video game industry may have substantially less choice among employers, and Microsoft may have outsized market power in hiring and retaining employees in the video gaming field, which requires specialized talent. [...] Concentration in the market may further limit employees’ negotiating power and ability to change employers for improved working environments and compensation," it said.

The complaint states that the merger of Microsoft and Activision Blizzard will irreparably harm competition because Microsoft is acquiring, and thereby eliminating one of only a few significant rivals of gaming content creation. This last point is interesting, because the plaintiffs call themselves Playstation users, so is that an admission that Sony does not consider it a rival of Microsoft or Activision Blizzard? 

The plaintiffs have demanded that Microsoft and Activision's acquisition contract should be declared null and void, and that they should be permanently restricted from going in this direction ever again. They have also required Microsoft to pay for the cost of the lawsuit, including a "reasonable" attorney's fee.