It's a long time that I take eyes on them.
The Idea is good, but the implementation is still in unstable phase.
The aim of the project raised many times during development, from w9x to NT up to XP...
The major criticism about the project is: what if someday a working system will disturb MS and they start to suite the community?
ReactOs can bring evidence that sources are not copyied from MS, but what about patents hidden in software?