Confusing user experience. It's like frankenstein's monster. SareX can everything, but you should spend a lot of time to understand how it works. Useful for complex professional tasks only, not for a common user.
But the point is that the Greenshot inside ShareX looks better (cleaner) than standalone one.

there is no linux version for this application and all other alternatives on linux are not even close to ease of use and feature set. for now my recommendation is screencloud for linux users.

I used to use Skitch for quick image annotating, but after Skitch was discontinued I found this as an alternative. The main thing I want for an image annotator is easy to use arrows and text with outlines. Programs such as Greenshot are good, but don't have text with outlines. This program does have it and that is why I like it.

Saw the Chrome tag, I went to add ShareX extension and found it only works with Windows and not Chrome. Evidently it works within a Chrome BROWSER and not Chrome the OS.

It has a lot of functionality, it's open source, it's relatively fast on my PC, and navigation is fairly straight forward.

ShareX seems to be a port of Greenshot. It has more options than Greenshot. However, Greenshot just feels much more "solid" when it comes to user experience. If Greenshot's options are enough for you, I would recommend Greenshot.

It is also quite true what one of the other commenters had said - the developers of ShareX seem to be very defensive when it comes to bug reports and feature requests.

The developers don't like bug reports or suggestions, it makes them defensive. (Not sure why they bothered making it open source.) And documentation is nil. Think I'll switch to Greenshot.

ShareX (and also Greenshot) cannot capture fullscreen directx (maybe also opengl) applications.
If you want to capture these applications, you need to run them in window (or borderless window) mode.