of course, (sprite-) size doesn't really matter and super mario bros. is still the far superior game of those two 
Cumulatively, I've played FAR more of The Kung Fu than Super Mario Brothers in my life, and to be honest it's a toss up on which game I've had more fun with as both have their merits. The most fun I have had with smb is making the game completely freak out with a game genie. On the flip side, The Kung Fu wins for the cheesiness and kick ass music alone. It's like being in an old nonsensical cheesy-great kung fu flick. To be fair that's what the game was going for, a parody of many kung fu flicks. It was supposed to make you laugh as you played it and certainly, just about every aspect of the game can be tied to some element of the kung fu movies it parodies. (Yes even the flying "potatoes"
) The game was not meant to be taken seriously, at least I think so.
It even mocks itself by having the title "The Kung Fu". I don't think the sprite size or gameplay were ever supposed to be it's main selling points, but over time sprite size has become the only reason people note. Personally I believe it's a lot deeper than people think.
Basically if you don't understand all things it parodies and subtle humor, or if you can't appreciate the general atmosphere of the game you are missing most of what makes the game fun. Perhaps their fault was trying to be a little TOO clever, and unfortunately nobody really caught on.
