Something that I miss from Paint.NET is the option to have the lines terminate with semicircles, rather than a flat face or an arrow. As someone who makes custom assets for the comic-making program "Walfas", this was a very good feature.

Of course, these days, I have moved on to using a Linux system rather than a Windows one, due to the latter giving me the worst performance issues I have ever encountered on any system. I have continued to make custom Walfas assets, but the quality tends to suffer as a result of not having rounded edges.

The option to end lines in a round fashion rather than a square or arrow would be a very simple change that shouldn't take long to code for, and would be incredibly useful, particularly for people who are drawing simple, cartoony versions of objects for use in a comicking tool.