I'm a big fan of Elementary OS and have been around since Freya. Recently loaded Loki to a new development box... I think it's great (after a bit of tweaking: ppa, gdebi, etc). Updates are current as of this posting.
Please take anything that appears to be critical with a grain of salt. Love the OS. Everything is mostly fast, sweet and very well designed. Not going anywhere...
That being said, I've had a strange recurring gui issue with Geary/Pantheon-Mail across both releases. Massive stretching that makes Mail impossible to use. Popped up after a few days on Freya, took a week or so to happen with Loki.
Interesting differences: Freya stretching occurred instantly (when it occurred); it was also very large, horizontally (can't really guess at the pixel width).
Loki Mail stretched almost comically: it started loading, then started stretching in front of my eyes like Stretch Armstrong (image below). I really like the email client itself, so it would be great if we could figure this out.
Is this a GTK issue?
Here's the money, with a terminal for scale: