Depending on the age group, I guess. I know plenty of people who would say that Windows had its peak usability around Windows 2000/2003 and only got heavier and more confusing later on.
If I know that ReactOS had a good chance of running most regular Windows applications, I'd install it on my mother's laptop in a heartbeat, and she would love to see the familiar, lightweight OS.
Frankly I can't think of anything they've added since 2000 to windows (except better security) that was an improvement.
I occasionally have to use Windows for work and I really hate Windows 10, it's just a chore to deal with when you only boot it every couple of weeks just on the updates.
I think the 'seniors' amongst us may well welcome ReactOS together with those in small companies who run legacy industrial hardware from Windows PCs (depending on stability &c).
Given Microsoft's mostly successful effort to make Windows more friendly to the user, I find it hard to believe any of these people have extensive experience with Windows 7+
Does the DOS stuff work? (NTVDM)
On a somewhat more objective note, there was a lot of criticism back when it came out. (Specifically, about "the bloat". Everything is relative, I guess; one can say that things continued to get worse and worse from Windows 2000 on, although some would swear that it was NT4 that was the best Windows ever - e.g. it ran in 16MB of RAM vs. Windows 2000 that raised the requirement to 32MB; for comparison, Windows 95 only needed 8MB.)
IIRC Microsoft was pressured by OEMs into making a lower tier of Vista qualified hardware even though they knew it really required more than that to work acceptably well.
I never personally owned or used a Vista machine, but my office has a couple of them plugged in for a showroom area where they cycle powerpoint slides, and oh my god is it painful if you ever have to touch them. IIRC they've got 512 MB of RAM, and some of that is being shared with the iGPU. It's not pretty.
512MB wasn't even enough for my WinXP box because the softeware apart from the OS became more demanding with time.
I remember installing Windows 95, from floppy disks back in 1996 or so. The system requirements on the box said 4MB of RAM. And it was true, Windows would run with 4MB. In the fine print, the box also said if you wanted to do anything besides play solitaire, like word processing, 8 was recommended.
So it's been going on a long time, the lowball estimate of systems requirements to get you to buy the product, then the real cost after you've already installed it. 4MB is a rounding error these days, back then it was at least a couple hundred dollars.
I find that Windows 2000 has the best support for keyboard users among GUIs. Better that MacOS, better than all the incarnations of Gnome/KDE, better that the following releases of Windows, that "forgot" about the keyboard and focused on other input systems.
You can see that in many small things, like sane keybindings and reasonable sequence for selection through tabs (for example, going from the path bar on the top to the folder content requires two tabs in Windows 2000 but four in Windows 7, unless one does some find tuninng of the UI).
The "mostly successful efforts" you speak of seem to have been focused on delivering ads, TOS-backed spyware and those weird Metro apps. The result is certainly simpler from a strictly visual standpoint, but more usable is something that I wouldn't be too willing to concede without some data (and I don't mean install data/user base, given how Microsoft's customers don't have much of a choice in this department). Frankly, I don't see how the weird start menu or having both the Control Panel and some weird Settings thing help with usability, but UX is a surprising field, I guess.