The ReactOS project appears to be trying to recreate the experience of Windows 95 through to Windows 2000 as faithfully as possible and, from a look and feel perspective, the developers have done an amazing job. However, from a practical point of view ReactOS rarely delivered the functionality I would expect from its closed source cousin. The system refused to run on either of my test machines and, though it would install in VirtualBox, I regularly ran into system crashes, sound didn't work and most of the Windows applications I tried to run failed in some way. I have had better luck running Windows software with WINE on Linux boxes than I did with ReactOS.
In the end, while I admire the ReactOS team's attention to detail in recreating the Windows interface, I do not think running ReactOS is practical for most situations. WINE will run most Windows software passably well and there are lots of good open source alternatives to most closed source applications. Running an old copy of Windows in a virtual machine would probably offer a better experience in most circumstances. The one area where I think ReactOS would shine would be if a person needed to run a Windows clone on hardware that also required Windows specific drivers. ReactOS reports itself to be compatible with drivers written for Microsoft's operating system and I think that may prove to be the project's strong point. Some old systems are very particular when it comes to applications and drivers and I think ReactOS might fill in nicely in those situations.