Pro Good web UI
GitLab's UI is clean and intuitive. Each view is designed to not fill the screen with useless information.
It displays the activity in a feed-type way in the most prominent part of the view. On top of that, there's a toolbar with buttons which can filter this feed by pushes, merge events or comments.
On the left, there's a menu that displays all the links that take you to the different views. For example, a file directory which displays all the files in that repo, a commit view which displays all the commits in cronological order, a network and a graph view that display important information graphically etc...
All these details make GitLab's UI extremely intuitive and easy to use, no view is overflown with information and every view displays only the most useful and crucial information needed at that time.