Mostly the fact that for the past 10 years they've been adding new features but never finished them and taken the time to properly bugfix them along the way. Just a few I ran into recently:

- Interface Builder is stuck in early 2010s. Not only is the property panel missing half of options we now take for granted everywhere else (like corner radius), it also randomly won't read fonts in the current project, will crash the entire IDE if you Cmd-Z a big change (things like unembedding a view) and half the UI is still not rendered the way it will be on the phone. Yes, Swift UI exists, but most bigger apps are still XIBs and Storyboards and it's going to remain that way for quite some time.

- Autocomplete is a hit or miss. Very much like the mid-90s Microsoft IDEs where you'd get totally useless results until you've typed the whole line out already. It can be done well, look at AppCode.

- Syntax highlighting feels pretty much the same. Randomly flashes on and off, often doesn't highlight until return is pressed, takes a long time to load on large files etc.

- Git integration is by far the worst I've seen out of any IDE and I've seen many. I'd go as far as to say that SourceSafe integration in VB6 was done better. Just the whole layout, modal-on-modal returning to the first modal on an error in the second and so on. It's crashed when rebasing a few times too, I don't trust it with larger operations since.

- Documentation browser is this annoying little window with semi-useful search. But don't worry, the docs in there are useless anyways. I could go on and on about their approach to docs but maybe next time.

Don't even get me started on performance. Things like switching file tabs should be instant by now but there are still noticeable delays for larger files and IB screens. Plus there's now two kinds of tabs (app-level and file-level) to add to the mess.