Yaaaay! Happy threads are my favourite kind!
Alright then;
-
The scope. There is NO other game that allows you to go from a blob in the pondscum of the universe into a being that can to an extent actually shape the universe around it. And this one actually works and has a genuine sense of connection from stage to stage.
-
The Cell Phase is much deeper and more entertaining than I expected. From the Pikmin-esque squeaks of the big-eyed blobs to the way in which the slightest alteration of where you have your fins, flagella etc. can affect the way you turn and move. I also love how whenever I cross the threshold and grow a bit bigger, I can cackle and chase the big bullies that are now so small and pitiful! Until, of course, the next behemoth paddles into view and I squeal and squirm away. Oh! And I love the Proboscis part, there is truly great joy in slurping the fluids out of things.

-
At all levels, the creatures always have personality. If I come back to my nest and one of my kind is feeling, uh, 'friendly', they'll follow me around waving hopefully. I wish real life courtship worked like that, it'd simplify a lot! When your creature lays an egg, as the camera zooms in so you can design the next evolutionary step, the critter itself does a little happy dance. Bless! I also love it when creatures are scared of you and scamper away as you approach.
-
The game is really, really big. Every time I pan out to the galaxy after a wormhole hop to get my bearings and see where I've ended up, I'm completely overwhelmed by the magnitude of it. Especially if my Home symbol is a little speck on the opposite spiral arm, faaaaaaaaaaaaaaaar away.
-
I can make anything I like, and even if I think it's awful someone else out there will enjoy it. That's an amazing accomplishment and really makes the creator-to-player dynamic more transparent and inclusive. Likewise;
-
There's always something awesome I haven't discovered yet. Every time I'm in space and I get a radio signal from a fresh, new star, I'm always almost at the edge of my seat as I zoom in and open communications to see what they look like.
-
Secret achievements. I'm going to try everything until I unlock one!
-
I can take a bunch of big-nosed stripey space-weasels and have them act like big-nosed stripey space-weasels should, and the game will cater to my playstyle. Space empires will grin as I line their pockets with the finest spices to keep them happy, and I can knock them the odd artifact or two (usually lifted from their own planet or a planet in their system) for a hearty cash bonus. I can dash down to Civ-level species on rare-spice planets and steal their blue or purple powders to sell to unknowing customers a few systems away, and there's nothing the primitive fools can do about it! I can (and have) go wormhole-hopping, get totally lost and spend the rest of the afternoon making my way back to my home system in a grandiose Voyager/Farscape-like adventure. And, in a nice little touch, when I bring my starship down to hover over one of my colonies, crowds of Vemnix gather around and cheer enthusiastically that the great
Ex Nihilo, Flagship Of The Collective has come to visit.

-
That 8-bit song some of the space empires play. It's so awesome!
-
Spore's potentially the best crossover game ever, because you can have entire worlds populated by Pikmin and Yoshis and Goombas and Lemmings and Norns and anything else you can think of, and see how they interact.
-
Terraforming is great, both as a weapon and as a bringer of life. I love seeding my newly habitable worlds with the creatures made by my friends at Gamingsteve.

-
Spore is actually very very funny. From the awkward silence after one of the advancing-to-Civ tribal critters suggests that their brave new world have an abundance of pie, to the fact that the other day I was hovering over an enemy tribe plotting my attack and was distracted with chuckling when one of the creatures, while his friends all stood idle with spears and grunted and the like, began dancing around in a circle, eyes merrily closed while he made, "Mmmm-ah-mmm-ah-mmmmah!!!" noises. For
ages. For no reason other than he could!
-
I love when you enter a star system and one of the planets goes "wooo-wheee-wooo-wheee-wheee-whee-wheee-wooo" and has little yellow lines coming off it. The scent of treasure! It's the same kind of enticing feeling you get while you haul up a treasure chest in
Zelda: Phantom Hourglass, find an unguarded chest full of loot in
World of Warcraft, or accidentally discover a hidden block with Mario's head. And just to cap it off, when you beam the relic aboard it's got a funny little description. Will's Old Sword FTW!
-
Even when I roll my eyes at the prospect of invading space pirates, when I zoom down to the planet and engage my weaponry I still have fun as I chase them around the globe and scream
"EAT ELECTRIC VENGEANCE, SCUM OF THE MULTIVERSE!!!" at my monitor as I shoot them down. But that's just me.
-
According to Spore, the centre of the Galaxy and the mysteries of life itself are guarded by small cybernetic goblin-monkeys. Never in any other game have I been so afraid of small cybernetic goblin-monkeys.
-
Wormhole hopping. It's just
the way to travel!
-
My computer's so old it actually runs off a coal furnace in a secret basement manned by a hideous waif named Igor, but I can still run Spore really well, much more effectively than The Sims 2 in fact, and it still looks good. Rarely do I have to call down, "MORE COAL, IGOR!!!" to get the framerate back up to speed.