I'm in the same position, I've switched from Sublime Text to Atom since January, but now I'm switching back to Sublime Text.
A few things that I expected and didn't quite make it, yet.
Speed - atom is quite slow, and I'm not comparing it with Sublime, I'm comparing it to other online IDEs which are build using the same tech.
Very buggy, the amount of open issues is daunting, I had some serious issues with vim-mode and the editor's buffer, was typing something pressed Shift+v, selected text, pressed another command and the console popped with an error, and what I selected was deleted and no way to use undo as everything I pressed gave another error. Went to report the issue and saw related issues open since a few months ago.
I really appreciate your efforts, I really do, but Atom needs a very stable and fast core.
The modularity it introduces through packages is extraordinary, but in my opinion was released too early. Developers jumped in and started to write packages, which was great, until you install a few of them and it feels like an IDE running in IE8.