Certainly a fan, and I don't understand the hate towards it.

Flatpaks are my preferred way of installing Linux apps, unless it is a system package, or something that genuinely requires extensive permissions like a VPN client, or something many other apps depend on like Wine.

The commonly cited issues with Flatpaks are:

• Performance. Honestly, do you even care if your Pomodoro timer app takes up 1 more megabyte of RAM? Do you actually notice?
• Bloat. Oh, yes, an app now takes 20 MB instead of 10 MB. Again, does anybody care?
• Slower and larger updates. Could be an issue for someone on a metered traffic, or with very little time to do updates. Flatpaks update in the background, though, and you typically won't notice the difference unless you need something newest now (in which case you'll have to wait an extra minute)
• Having to check permissions. This is a feature, not a bug. For common proponents of privacy and security, Linuxheads grew insanely comfortable granting literally every maintainer full access to their system. Flatpaks intentionally limit apps functionality to what is allowed, and if in some case defaults aren't good for your use case - just toggle a switch in Flatseal, c'mon, you don't need any expertise to change it.

What you gain for it? Everything.

• Full control over app's permissions. Your mail client doesn't need full system permissions, and neither do your messengers. Hell, even your backup client only needs to access what it backs up.
• All dependencies built in. You'll never have to face dependency hell, ever, no matter what. And you can be absolutely sure the app is fully featured and you won't have to look for missing nonessential dependencies.
• Fully distro-agnostic. If something works on my EndeavourOS, it will work on my OpenSUSE Slowroll, and on my Debian 12. And it will be exactly the same thing, same version, same features. It's beautiful.
• Stability. Flatpaks are sandboxed, so they don't affect your system and cannot harm it in any way. This is why immutable distros feature Flatpaks as the main application source. Using them with mutable distributions will also greatly enhance stability.

Alternatives?

AppImages don't need an installation, so they are nice to see what the program is about. But for other uses, they are garbage-tier. Somehow they manage both not to integrate with the system and not be sandboxed, you need manual intervention or additional tools to at least update them/add to application menu, and ultimately, they depend on one file somewhere. This is extremely unreliable and one should likely never use AppImages for anything but "use and delete".

Snaps...aside from all the controversy about Snap Store being proprietary and Ubuntu shoving snaps down people's throats, they were just never originally developed with desktop applications in mind. As a result, Snaps are commonly so much slower and bulkier that it actually starts getting very noticeable. Permissions are also way less detailed, meaning you can't set apps up with minimum permissions for your use case.

This all leaves us with one King:

And it is Flatpak.