Spore Galactic Adventures brings all the good from the Creature Stage and adds a bit action to it.
Those who played it, will agree that the space stage was very boring and one-sided, clicking on one yellow/red point after another and stuff...with Galactic Adventures, Maxis wants it to be more interesting, as it adds little series of quests. The difference is, that you're not in you're spaceship as always...you're on the planet with your creature you created!
The quests mostly change in their base...sometimes you only need to talk, sometimes you need to kill everybody's cat. First in line is the fact, that you finally are your creature.
There are 42 new accessories, with which you can equip your creature. These accessories bring your creature new skills like health-regeneration or new ways of attacking.
The adventure creature allows you to create your own adventures...sounds difficult but it isn't...You can do everything through drag&drop.
What I disliked was the fact that you really need to look for an adventure...I spent a lot of hours, flying through the orbit just to find ONE adventure (although I downloaded some additional adventures from the Internet) . In addition, a few of the adventures are simply too difficult for some creatures...because of the individual quest goals, the expansion needs a balanced creature (social and aggressive parts are needed). I had a lot of problems with my Anura-species, which I always played as a Warrior.
To sum up, Spore's first game-expansion is very averaged. It's a lot of fun, creating your own adventures, but like the creature creator, you will have enough of it after a while.