I'm slowly working my way through season six on DVD and have just now watched this for the first time. A nice experiment. Great to see some of the regulars out of makeup and prosthetics and in new roles. It doesn't have the most original premise or the most profound insights, but overall I think it was up to DS9's high standards.
Sisko/Russel's breakdown was a little bit funny, but I think just short of going over the top considering the circumstances. Brooks has done a lot worse (not that he doesn't usually turn in a good performance).