Spore is not 1 game, it is 5 different games. The first one is a mildly interesting version of the old worm game. Nothing brilliant, but certainly entertaining for a while. The others are bad, they get progressively worse and start out pretty awful. Even the creature creator is bad, it specifically limits your ability to make a complex or extravagant creature, but it is very easy to make an incredibly dull creature that has the maximum capabilities. So it limits the fun and creative aspects, and has no challenge in the difficulty, it is the worst of all worlds. And of course, let's not forget that they manage to squeeze in the classic grinding for xp as you wander the island pointlessly searching for new parts and points, which almost never actually give you a new ability, they just make a slightly larger change when they affect a status bar if they do anything at all.
Stage 1(worm): interesting so long as you don't spend much time on it. Actually fun, this is me talking about what I like about it.
Stage 2(RPG): repetitive, pointless, no reward for creative or intelligent efforts. Carry over from stage 1 will probably be gone after a few minutes.
Stage 3(RTS): repetitive, obvious, a couple of abilities can carry over from stage 2 only flying is significant.
stage 4(RTS): tank rush... no carry over from previous stages
stage 5(RPG): You are the only intelligent being in the universe, too much micro, no scaling at all, no competition, waaaaaaaaaay too much grinding. no carry over from previous stages.
Spore is five different games, and there are much better games out there that do the same thing, with the possible exception of the first which is an all but dead genre. The only thing in its favour is that the games are connected, but the connections range from obsolete to nonexistent. Spore is a dud, sometimes people play duds, but don't think for a second that it is competitive... Oh, and the online sharing bit, which from my experience was used only just enough for people to share anatomically correct creatures, but not enough to avoid seeing the same few creature endlessly repeated...