As you might guess, you're not really being given a game here. Spore: Galactic Adventures is a toolkit used to make games, using blank worlds as a staging ground. It's impressively flexible, allowing you to play through adventures using your own custom-evolved hero or one determined for you by the scenario, and to create your own custom adventures with which to befuddle your friends.
In Galactic Adventures, you begin with a blank world and a large number of tools you can play with. One of Maxis' employees was killing time at a recent EA event in San Francisco by designing a birthday party-themed level, with confetti generators and playing clowns; other adventures were set in a tiny universe, with the player's character standing atop a planet like the last level of Katamari Damacy and jumping from star to star, and on a battlefield, where two alien races were shooting it out for supremacy. The player's job in the latter scenario was to get behind enemy lines and figure out a way to get onto his opponent's mother ship in order to prevent them from constantly teleporting in reinforcements.
The real draw with a game like this is going to be what the fan community does with this, and it should be something to see. You can not only develop your own adventures and worlds in Galactic Adventures or play through Maxis' prepackaged adventures, but you can also develop your own objects to place within that world. With time, you can generate an entirely new universe using the same toolkit, but it could look nothing like anything that anyone else would create. It's intuitive and flexible, with pre-existing objects ranging from simple walls and floors to party supplies, planetoids, enemy characters, tracked vehicles and entire starships.
The gameplay I saw, as a Maxis employee played through the aforementioned mother ship scenario, was a bit basic. Your combat abilities in a scenario are determined by what you're allowed to play; the adventure designer may let you bring your own customized monster or limit you to a preexisting character. In this scenario, the player's given a specific monster, complete with a plasma gun and jetpack, and set loose to accomplish his mission however he can. The combat's actually somewhat reminiscent of RPGs, with the player and opponents exchanging fire and the loser being the guy to run out of HP first.
I have to admit that the adventure I was shown seemed shallow. It's an introductory scenario, though, and the real test is going to be what starts coming out a week or two after the game launches. Galactic Adventures is a game that's hard to cover because so much of its appeal is based upon what's done with it, rather than what it offers. Even the basic toolset can and probably will be improved upon after its launch. Fittingly, Spore: Galactic Adventures will evolve after its release, and half of the entertainment's going to be seeing what happens with it next.
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