To me, the biggest feature is https://about.gitlab.com/2019/04/22/gitlab-11-10-released/#s.... I've seen so many repositories imitating custom fields with labels starting with the same prefix, having it enforced by is such a good thing.
I love using Gitlab as a part of development cycle, managing issues and handling pull/merge requests but per seat licensing is a bit steep for a single user, even more so for a team.
The norm for pricing products and services is more and more "just for a pint/coffee/sandwich a month" but when everyone wants their share of the cash, the end result is a mismash of services and products that don't work together well (if at all) and you get stuck without a pint/coffee/sandwich for the whole month now.