A snippet from GameSpot’s preview on Spore’s first expansion:

In addition to actors, you’ll naturally need to build a story for them to work within, and you’ll be able to add text for each character and basic cutscenes. When you’re creating adventures, an onscreen meter will tell you how complex your adventure is, and this will fill up as you add more items until it eventually reaches its limit. To create and play in the new adventures, you’ll need to purchase a copy of Galactic Adventures and get to Master Badge level 2. Maxis has bundled in 20 “really good” missions to get you started, although we didn’t get to see them at the event, and if you’d prefer to create an adventure for fun, you can remove goals altogether and roam at leisure. The game is currently still in alpha, and the team is looking to include yet more features before launch, such as the ability to edit other creators’ adventures, a classification system in Sporepedia for adventures (difficulty, age rating, type of adventure, that sort of thing), and possibly the ability to drive vehicles in the game.

GameSpot – Spore Galactic Adventures first impressions