No syntax highlighting on diffs, horrible defaults (closing development branch when you merge into master???), not being able to make a PR after you make one commit to a branch without refreshing and loosing your message, inconsistent code formatting that is just horribly broken in general, weekly downtime that's not reflected on their status page, having to manually press a button to see updated diffs after updating a branch, no support for signed commits, API support lacking in the weirdest places, random failings in commit webhooks, etc etc.
God I hate it.