I have not heard any Falkenbach, so can't really speak about them.
I found Windir to be mostly boring... the odd song has a catchy riff or too, but I found myself quickly disinterested.
The Mithotyn stuff I've heard sounds more interesting than Windir, however, I have not heard that much. A few of them did a side project called "The Choir of Vengeance", basically them doing raw BM. It's pretty bland.