C&C per req:
1. I like this; nice monochrome conversion, but it seems slightly under-exposed. I would also like to see just a little more detail in his hair.
2. I think your lighting just missed on this one. It seems about 1/3 stop too hot on the strobe side, and about the same too dark on the unlit side. A reflector image left would have helped here I think.
3. Not bad, great expression, BUT again, the dark side seems a bit too dark to me.
4. Not as fond of this one; he has a serious case of racoon-eyes and a reflector low and image left would have helped a lot.
Overall, these make a nice set. Your lighting is good, but still has room for improvement. Keep shooting.
Just my $00.02 worth - your mileage may vary.
~John