I am a GitLab user and have been for about 2 years now. With that being said, I think this acquisition makes a ton of sense strategically. Microsoft has really been trying to change their identity from being a stuffy close-source corporation to an open company that developers can rely on. And they have done pretty well at this. They open sourced .net, run MS SQL on Linux, and have released the WSL (which would have been unfathomable a decade ago). They also moved their VCS over to Git for Windows development.
GitHub, however, has a business issue of not making money. I think with the resources that Microsoft can provide GitHub can continue to build a great product and tap further into Microsoft's enterprise user base to make sales and release more features that customers want/need.
Congrats to everyone at GitHub for this momentous acquisition!