For me as a PC gamer, this means Microsoft is more than ever invested in making gaming work, and their efforts at making PC gaming work have never been more ambitious. Since Activision's titles were already on PC though, there's no direct upside on this front.
For me as an (occasional) Game Pass user, this means more cool games available to play freely, at a relatively low cost. That's going to be a positive, as I think game passes have a solid future as part of the hobby. I don't see an MS Game Pass coming to Steam, so that's something that's on my mind, but I've always been open to platforms and stores if their offer was solid.
For me as a Playstation gamer, it doesn't mean a thing: I only play on Playstation when the exclusives are worth it. Having exhausted the PS4 exclusives I cannot resist, I've even sold the console.
From an industry point of view, I've always thought Microsoft needed a much stronger in-house capability to challenge Sony's exclusives. However, I always thought that meant attracting studios and new IP, not buying up existing studios and IP. Exclusivity isn't a very cool thing for gamers in general, and having several behemoth franchises and studios move toward MS and away from Sony doesn't add to the market, it takes away. Even if that doesn't have a direct effect on me and my gaming habits, from an industry point of view I don't think this is a positive development.