Mr. Big was an excellent starter episode to an iconic series. The story was well developed and nicely paced. The major characters to whom we are introduced, Max, 99 and the Chief enter the episode fully in character as if we had just been privy to a what a day would be in their, to them, perfectly normal lives.
Max, Agent 86, is a well meaning, if only slightly inept and barely secret, Agent for Control, He bounces back and forth between brilliance and pratfalls and introduces us to some of what will become classic lines, "that's the second time I fell for that....", "would you believe...".
99, stunningly beautiful and mostly under-appreciated for her contributions to the success of the mission.
Chief, the long suffering leader of Control, an international Agency based in the US and reporting to the President.
Further, we are treated to an array of barely functional gadgets that will reappear over the life of the show. The Cone of Silence, the Shoe Phone.
There are far too many gags to list and I wouldn't want to anyways because they truly need to be seen to be appreciated. The comedy that came out of Get Smart would set the stage for many comedy shows and movies to come. Mel Brooks and Buck Henry had brought farce and satire to television comedy that had previously been mostly formulaic.