It can be an improvement on Microsoft’s offering in some ways, but it’s also problematic in other ways. The open-core is without a doubt better than being fully proprietary like Microsoft GitHub, but it’s also not fully open. GitLab is based in the US & is publicly-traded meaning it has to comply with US sanctions (which can ban some of your contributors) as well as needing to prioritize value to shareholders--not users. The architecture is also a bit of a mess being built on slow Rails servers & sluggish React clients (+ requires JS) meaning the user experience is not snappy. I also hear (as I’ve never self-hosted) that migrations, scaling, & maintenance isn’t a fun experience with the service. There also might be too many features in the service you aren’t using but now have to support.

If using Git as your VCS, one may want to take a look into cgit, Forgejo, Gitea, or SourceHut as alternative before committing to GitLab. You may also consider alternatives to Git too!