I agree with the original poster on everything except the score. The game definitely deserves a 9. The reasons it has been getting worse reviews are: 1. It is not the game everyone was expecting. 2. It doesn't live up to its potential (or its hype). 3. The early stages are awful, and poorly integrated (some people have described them as tutorial stages. They're not. The control scheme and gameplay mechanics are completely different from the Space Stage). 4. It is riddled with nonsensical design flaws (and despite what some reviews have said, a number of annoying bugs).
So why does it deserve a 9? Well, most people would agree that the character customisation is unparalleled, and the way the game integrates user generated content is incredibly innovative. It is also a great 4x RTS. Sins of a Solar Empire was widely praised for the way it incorporated the design of a 4x game into an RTS format, and Spore essentially does the same thing.
Reviewers claim that it lacks depth, which is undoubtedly true for the early stages, but although the Space Stage may have less complex gameplay mechanics than something like Civilization, it has a lot more depth than the average RTS. In fact, it is better than many highly praised strategy games of the last few years, such as Company of Heroes, World in Conflict, and especially the wildly overrated Supreme Commander.
To all the people saying they quit playing before or soon into the Space Stage: do not judge it until you have played the Space Stage for several hours. I played the game for most of the weekend, and for the most part, I was massively disappointed, bored and frustrated. After playing the Space Stage extensively, I am all turned around on the subject. If you had to play from the cell stage every time, the game would deserve a 7. But you don't. If the Space Stage had been released as a standalone game (with the creation tools, of course) without any hype surrounding it, it would have scored much better reviews.
Personally, I think the game should have been made into a trilogy: Evolution (cell & creature), Civilization (tribal & civ), and Exploration (space). Instead it like the third part of a trilogy, with the first two parts condensed into some shit mini-games.