It's a very impressive project with very niche use. I think it's pretty clear that it would be good to have a FOSS system that's compatible with old Windows, especially since we live in a world where Windows XP has become one of those critical legacy techs that never quite go away, like fax machines.
At the same time ReactOS is sometimes disappointing as you say and feels like it's never going to be usable. In late 2023 now, it still rarely runs on real hardware at all, and is missing lots of features you had twenty years ago in XP. USB 2.0 is only supported partially, USB keyboard support is incomplete, wifi only supports WEP authentication, which has been deprecated for the same twenty years, etc.
I admire the project for still continuing with what's an extremely difficult task - they're reimplementing the NT kernel and some major userspace programs like explorer.exe but at this point I don't know if I believe ReactOS will ever reach parity with WinXP. I just checked and they still don't have RW support for NTFS, which was the default file system for XP in 2001. For Linux, ntfs-3g was fully RW in 2007.
Going by how long ReactOS is developed and how unuseable it still is I wonder if the time would haven been better spent decompiling windows 2000 and structuring the code. Once that is done you have a solid base to modify and modernize the OS however you want.
No need to decompile Windows since there have been substantial code leaks, and more recently the entire (or near?) WinXP source leaked. It's even on GitHub.
The problem is of course that anyone using the source code would be in legal trouble, and ReactOS has a policy of not accepting contributions from anyone who has as much as looked at the actual Windows source. How well they maintain their clean room is an open question, but an OS based on leaked or decompiled code would definitely be getting sued into oblivion.
At the same time ReactOS is sometimes disappointing as you say and feels like it's never going to be usable. In late 2023 now, it still rarely runs on real hardware at all, and is missing lots of features you had twenty years ago in XP. USB 2.0 is only supported partially, USB keyboard support is incomplete, wifi only supports WEP authentication, which has been deprecated for the same twenty years, etc.
I admire the project for still continuing with what's an extremely difficult task - they're reimplementing the NT kernel and some major userspace programs like explorer.exe but at this point I don't know if I believe ReactOS will ever reach parity with WinXP. I just checked and they still don't have RW support for NTFS, which was the default file system for XP in 2001. For Linux, ntfs-3g was fully RW in 2007.