I guess now the kernel is written in C++. I didn't look at it but if it's true, it's probably very different from the sources from MS. And anyway the snippets I compared between Reactos kernel source code around 2005 and Microsoft source leaks, shown they were quite different. And if you look at really old Reactos code (pre 2.x), it is very very different from the code found later. So it could be argued that there was a continuous progression, which would not be the case if they had used heavily MS sources (legal and leaks). And a lot of code comes from other open source projects, for example the USB stack was imported from Haiku.

I also expect current Reactos developers much less "adventurous" than some older developers.

Anyway if you use Linuw + Wine (or Codewaiver or alternatives) you have a good OS plus good Windows compatibility.