I tried that yesterday because the ISOs were already up and unfortunately, unless Qemu is an unsupported platform, it's a mess.

First, I tried the LiveCD and found that the default qemu's network driver is unsupported. Found the docs, changed the driver and found that I have networking... but explorer.exe can't really visit any page, so all I could think of is to telnet somewhere. Then I tried to install some apps, but found that the "add or remove applications", while being a nice concept, unfortunately doesn't work on the live CD. So I switched to the main iso.

Two reboots later I tried to install Firefox... and found that it freezes the machine. A while later I found that this is the way ReactOS handles lack of RAM, so I added some. The scary part is that the freeze actually rendered the system unbootable after restart, which is super weird. Then I was wondering if I could install some old Visual Studio there and while trying to install .NET, first I found that 4.6 is "unsupported on this system" (which is fair, since it's fairly new) and the older .NET crashed the system again, this time because I ran out of disk space. So, if the system runs out of resources, its default response is to bluescreen.

At this point I just gave up. I'll probably come back to try it out at the next release, but for now... either I'm doing something wrong, or it's unusable.