annabelgray
Our navigation was redesigned about 2 years ago (https://gitlab.com/gitlab-org/gitlab-ce/issues/32794), and we conducted a lot of research and user studies to ensure we were creating the best possible experience (https://gitlab.com/gitlab-org/gitlab-ce/issues/34917). All the navigation items to get to different pages within a project are contained in the left sidebar, while the buttons on the main portion of the screen are directly related to the current page.
For the issues page, I agree; we should probably add a max-width to the list. I've opened an issue to try it out https://gitlab.com/gitlab-org/gitlab-ce/issues/61046
We're currently also in the process of rethinking the right sidebar. It's getting cluttered, and there are items in there that probably aren't as frequently used as others. I've opened an MR to test a new design idea- https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/27752. We're also conducting research to find out which items are most frequently used/most important- https://gitlab.com/gitlab-org/ux-research/issues/134 (the issue is private, but will be made public once the studies have been completed).
Hopefully this addressed at least some of your points. Please feel free to open some issues with any other ideas you have.