It is an add-on, not a sequel . . .
The Sims is a world where you control almost everything about your character's life. You choose their employment, their decorations of the house, who they fall for, and every little move from dawn till dusk. The expansion pack adds some new equipment and new skins to play around with. It also provides the same great interactions that you have grown to love, with a couple new emotions and reactions.
Where the game falls short is that it cannot stand alone and contains many of the same problems that the original had, such as poor movement across the house, mediocre intelligence of the sim to know where you want him or her to go, and no interaction with the working environment.
That said, it is an expansion and does good for what it was meant for.