After reading the original play I thought it would have been much more difficult to adapt to screen than it turned out to be. Donal McCann puts in a once-off great performance as Public Gar, the repressed antagonist who is manifested openly on screen by his extroverted (but unseen to others) alterego- Private Gar. Eamonn Kelly also plays an excellent "screwballs" whose inability to communicate his feelings is matched only by Gar.
Definitely worth renting out if you can find it. (Probably unavailable outside Ireland & UK)