I played some Spore today. I decided that, above a load of other things, I have two main problems with it:
#1 is the lack of continuity between phases. Every time you move on to a new stage, everything is wiped out, and you can't ever go back to re-play it. A whole new set of creatures appears on your planet, and of course there is no real evolution (see point #2) which adds to the randomness. Aside from your city plans continuing from the civ stage into space, there's absolutely no way to leave your mark on 'your' planet. You get your basic species traits, but there's no sense of epic-ness. I really miss that after playing games like civ4, EU2, and NES forum games here on civfanatics, where worlds evolve over time and have layers of history to them.
The Sims and Sim City also that have continuity, the sense that you were building something up over time, not just accumulating X points so you could skip to a whole new scenario.
#2 is the AI competition. IMO, Spore puts itself in an awkward position with regards to this. In the Cell and Creature stages, you are 'special', nothing else can evolve or do the things you do. Tribal seems is impossible to lose. Civ stands out as being challenging, where other civs can defeat you (although I've yet to see anything other than brute military force achieve final victory, and it seems odd that your whole game ends just because your chosen faction didnt win

). In space, the fact that you play catch-up has fairly been called a refreshing change from other games, but in this case it also means the rest of space is pretty much stagnant. The other empires do slowly expand and fight, but again you are the only one with the special ability to expand rapidly, and the special spaceship and its special gizmos doing the special quests. Basically, its just a matter of perseverance/reloading before you get what you want. If you want anything at all.
In Civ4/EU2/Moo2, etc, things are more dynamic, you have rivals at different times, who do the same kinds of things you do. You compete for territory and influence, and new technologies can change the way the whole game works. You aren't the special chosen race and its not a linear progression - if you want to be the top empire, you have to struggle throughout history to get there, else others will overtake you. Or you can set yourself your own personal goals instead. I like the fact that you can end a game as 2nd or 10th in overall ranking, perhaps as an ally or vassal of strong AI players, and still feel like you had an interesting game.
On the other hand, in the Sims/Sim city, the only things you don't control are random disasters and briefly-encountered things. You don't compete with anyone except yourself, to create the kind of city/neighbourhood you want, or perhaps to match the achievements of some other player in another game. That is fun in its own way.
My point is, Spore has AI competition that basically just makes up the background, which could work well for an open-ended 'god' game, but in Spore's case the player is quite limited in action and has a linear set of goals set out for them, so the whole thing is quite unrewarding, IMO.
*Insert epic list of suggestions here*
I realise I want a whole new game with a whole new way of playing. No X-pacs are going to come close. I think I will be waiting a long time.

I guess your son is getting the full benefit of the way Spore was slimmed down and presented. Certain persons like myself have only become more demanding after wasting obscene amounts of time on computer games throughout their own childhood
I wonder if your son would like it so much if he had as much time to play it as he wanted... Not that I think it would be healthy, but I think one of the reasons I have fond memoires of Sonic the Hedgehog 2 was that I didn't have it (or a megadrive/genesis) but my friend did, and so I could only play it at his house, and in two player mode, which made it special
Ah those were the days, when your whole game would fit in a 2 megabyte cartridge...