First of, we're dealing with a pretty awesome concept for a game here. The development of life, from cellular to space faring species, with the player driving that evolution, with everything from the creature itself to buildings and vehicles. Just a space exploration game of the scale Spore is would be pretty good (I know other space colonization games exist, that's not my point), and I'll give it to Maxis for creating a large galaxy. However, it doesn't matter if that galaxy isn't filled with ... anything of interest. Colonies are bland, you can't really do much with them. You can only have a small fleet, not micro manage a whole array of ships (which is at least what I presumed, at least compared to civ phase, albeit that was on a small scale). Now, if you add that to the extremely cartoony graphics and very boring editing abilities that could have been so much more, it's very disappointing to see Spore. Every phase is hollow, lacking content, and you can't strap together five phases without content and call it content. That right there is Spore's problem.
Most of that was directed at space phase, but it is, and rightly should be, a prominent phase of the game. Saying "I saw reviews and gameplay" is nothing, and the only real way to feel the lack of actual content is to play the game.