What made this show great was that it was NOT completely a comedy...
What made GET SMART unique as a show for not only the 60's but for even today was that it was actually a Action/comedy.
How many other comedies of the time(or even today) can you think of that had genuine intense adventure and suspense with characters actually getting shot, stabbed or killed? And the series even had suspenseful cliff-hanger episodes not usually found in other comedies of the time.
If you took out the slapstick buffoonery what was left was a competent tho' light-hearted adventure series in the mold of 'The Avengers' with Patrick MacNee and Diana Rigg, also a tongue-in-cheek show.
And what kept the comedy balanced was that Maxwell Smart was not completely an idiot. In every episode he demonstrated courage, resourcefulness and the ability to think on his feet. And he was a good shot and good in a fight.
Its just that he would alternate between these moments of cunning with moments of tomfoolery.
As for 99(Barbara Feldon) and the Chief (Ed Platt) was that they were the perfect 'Straight' man and woman for Don Addams. Barbara was perfect as the frustrated but adoring 99 and Ed Platt had some terrific facial expressions of sheer exasperation!
I sincerely doubt the show would have lasted as long as it did if it was a pure farce.