A huge difference is that a queen, like a rook, can attack a whole row and column, making it possible to box in an opponent's king. A knight has limited reach

A huge difference is that a queen, like a rook, can attack a whole row and column, making it possible to box in an opponent's king. A knight has limited reach and can never attack a square the same colour as the one it is occupying. Another is that a queen, like a rook, can reach any unblocked square in at most two moves. A Knight can require up to six moves! Add to this the ability to move and attack diagonally like a bishop, but without the restriction of staying on the same colour of squares... The queen is immensely powerful.