- Use of space: GitLab uses vertical space inefficiently across the site. Elements have a bit too much padding for my tastes and are spaced a bit too far apart. Valuable screen space (top center) contains a lot of needless information on GitLab (table headers, project ID, language breakdown, a prompt to add a CONTRIBUTING file) which is either not present or located off to the side on GitHub.
- Color and typography: GitHub is one of the best sites at this, using pops of color for important buttons and really fun typography. I love how GitHub has your avatar "speak" a commit description, it's a great little touch. GitLab's design feels like it has less personality. Quick comparison: https://imgur.com/a/Ejd1Q1X
- Attention to detail: A bit less of it on GitLab -- icons and text don't vertically align in some places; several of the dropdown menus could use a bit of visual improvement, or have an ill-fitting item or two; in my screenshot above, GitLab's "Commit message" and "Target Branch" have inconsistent capitalization.
The performance is sluggish.
There's always a lot of buttons and stuff on the screen that most users will probably never use, making the UI cluttered.