The UI might look outdated, but on the other hand it's light weight and fast. There are a bunch of fancy text editors out there that are simply a resource hog.
The "huge row of inscrutable icons" school of design fell out of favor for good reason – while a few icons (like "Back" or "Close") can be immediately recognizable, when you get to that many, most of them are icons people haven't seen before, and people end up mostly not using the buttons at all. Even if they _are_ recognizable, who wants to hunt for icons in a huge list? So they just sit there, taking up space.
Hunting for them is no problem, after a few hours your muscle memory takes over. In fact, now I look at it, I like how this small amount of color provides a bit of recognizability and identity to the application as a whole.
All of this is tiny compared with just about any other application. Vertical pixel size is small. Horizontal size has plenty left over for more icons. You might have a point when talking about ms office around 2000, but not notepad++
You can get a description of the icons by hovering with the mouse pointer. The actual reason this style has fallen out of favor is to enable touch interfaces, which demand physically larger targets and do not generally support hover.