It depends on what you are looking for in a game. Spore is a completely unique gaming experience. The gameplay itself is not very deep, but it takes different genres and combines them effectively around a core of user created content (the characters, buildings, and vehicles can all be created). The online features are pretty awesome. Its great seeing one of my friends creatures running around in my game.
While I was always excited about spore, it was not my number one game on my list for this fall, but it was high enough that I considered it a must buy.
If you are looking for something unique, and enjoy creating the content of the game, this is for you, but if its not and you can only buy one game this fall, you may want to consider something else... crysis warhead (if you can run it) l4d, fc2 and fallout 3 are all coming out very soon, so if it depends on your budget and what kind of game you really like.