Its really impressive. Its kind of like in Trek, where Rene Aubergenois managed to inject real human qualities into Odo, making him more multi-dimensional and in the process enrich an on-paper stark authority figure. I can't imagine Michael Pillar ever even dreamed of where Odo would end up at in season 7 in terms of character development, lets say.Yeah. That's what's so impressive about Courtney. He took what, on paper, was your standard hidebound, unimaginative, warmongering authority figure that I'd normally have no respect for, yet made him charming and sympathetic. It's a classic illustration of what an actor can bring to a role. (Although so is the Doctor, really, given that it's all about each new actor making the character their own, reinventing the style while the substance stays essentially the same.)
My only gripe with Courtney, and its not with him but the writers of the show... He's superfluous in Battlefield. Worse, he's actually detrimental in trying to establish a new authority figure in Brigadier Bambera. So much so that he doesn't even die when he was supposed to. Similarly, it seems "criminal" to me that RTD never brought him to the show, although that might have to do with the era he was most influenced by, but still... series 4 could surely have had him at a guest spot? In the Sontaran two-parter maybe?
Oddly enough, one of his best post-show appearences as the Brigadier is really the rather professionally-but-still fan-made Downtime (and even more ironically, Sarah Jane is in there, but she is rather superfluous!). Love that production to bits.