A good combination of both structures
The game obviously follows the story of the 6 star wars movies, and includes some bonus levels not seen in the movies such as bount hunter missions etc. You can take control of any LEGO Star Wars character in free play mode and re-do a level to get all those hidden secrets you missed before and complete as much perent of the game as possible, the reason i say this is because LEGO games have allways been made to have tons of replay value, and this more so, there are more secrets, more levels, and more power-ups for you to find and explore, and it will take months for you to complete the game 100%.
In the end LEGO Star Wars: The complete saga is a great game with tons of fun, replay value and humor strapped on to it, along with extra missions, characters and vehicles, this is a must have for any LEGO or Star Wars fanb alike. 4 STARS!