I got the chance to try out setting up an AppImage app for my brother, and now I can say that it has an absolutely awful UX.

AppImages are just apps and their libraries bundled into one file. You download it, you run it. Simple enough, right? However, the caveat is that these files are likely not marked as executable when you download them.

Scenario: you are a new user to Linux. You go looking for an app, and see that it has a download. You get the AppImage, open your file manager, then click it. Your computer will tell you that there's no way to open the file. Where do you go from here?

AppImages rely on the prior knowledge of how the executable bit works and how to set it. Users without that knowledge will hit a roadblock, and that's not the only one.

From what I know, AppImages are supposed to offer to set up a desktop file for the application on first launch. This one didn't do that. So, a new user might not know they need to go back to the file each time they want to run the app.

In addition, there are updates to worry about. If an AppImage'd app doesn't check for updates and you don't know you need the AppImage Update app installed, you will never get an updated app. A file from a website, like in the case I came across today, might have no indication of what you need to stay up to date.
I also take issue with the architecture of AppImage in comparison to flatpak. By default, AppImage is unsandboxed. There's "optional sandboxing", but I doubt users will put effort into installing another program and setting up sandboxing manually. If the goal is to protect users, sandboxing needs to be a seamless default.

@brainblasted I don't think a design goal of AppImage is to protect its users. Rather, the point is to get the application running regardless of the distro.

I'm using several AppImages all the time and they're working quite well.

@paperdigits I think it should be a goal. Sandboxing is important, especially if you're downloading and running binaries from different websites.

flatpak also should work regardless of distro.

@brainblasted I don't know if it *should* be a goal, but it isn't and they recommend firejail to do the sandboxing. AppImage has been around a long time, it is certainly the oldest of the new packaging formats.

For me, it has been nice to have a new GIMP package with some critical plugins included.

It makes testing new versions of apps easy, and there is a clear path back to the old version when the new one doesn't work.