(Actually game-s, I am not asking about THE most creative-based ONE....)

While I'm waiting for a dramatic promo on Scribblenauts (on gog I might have bought it at a higher price), I'm wondering :

What games do you know, on gog or elsewhere, that do actually demand some amount of creativity from the player's side ?

Such games seem rare. What I can think of is :

- Fantastic Contraption & Incredipede (I used to be very inventive on FC online, I'm lame nowadays on the Incredipede version).

- Incredible Machine series, I suppose

- World of Goo (and such Bridge Construction games), though I assume solutions end up looking much alike

- Crayon Physics

- Evil Genius maybe, and such trap-building games that allow you to invent new combinations

- Creatures, theorically but I never grasped that game's mechanics

Is that all ? Any other 'canvas' game you know were you can -or have to- invent and create a bit in order to progress ?

Dungeon Keeper 1&2 perhaps ?

Perhaps, but I never really had the impression of 'inventing' something, with them. Or making anything very personal. It felt more like mere management or tactics...

I do suppose that some people manage to do creative things with city builders, such as Sim City or whatnot, though...

Minecraft is kind of the canonical example lately, and I'd say that if you don't approach it as a creativity playground you're probably going to be disappointed by the depth of the rest of the gameplay and combat. I hear 2D games like Terraria and Starbound are fairly similar but I haven't played them yet so I don't know to what extent creativity is possible.

Bundle Stars has a Complete Crazy Machines bundle for $3.49. Haven't played it yet and I've seen that some people prefer the original Incredible Machine games, but it seems like a good deal for the price. On the other hand, the recently released Contraption Maker seems to be very well received so far.

Also, strategy games and especially city builders to some extent. I'm playing the original Tropico right now and it's nice to have control over how you want to structure your city, how you want to rule, what economic activities you want to pursue, etc.

Hm...challenging topic! Aside from Minecraft type of sandbox games I can't think of many games that demand creativity from the player's side straight out of the box. In fact, I'm drawing a complete blank here...

Level editing, making 3d models & textures and creating mod content in general etc is 10 times more creative than what one usually does in-game. Games are entertaining yes, but demanding actual creativity? Tough one.

EDIT: I felt pretty creative the first time I played Sim City Classic back in the day but that was more of an illusion of creativity.

Also made some really funny & weird levels with the Warcraft 2 editor but the options are somewhat limited.

I guess one good symptom of it would be, nowadays, how eager people are to show off "their own" solutions or constructions on the internet.

I feel that there's been more people showing their Sim City constructions than, say, their Stronghold castles or Tropico islands, but I'm not sure why, actually...

SpaceChem? It's problem-solving rather than sandbox, but it asks you to take a few simple elements, and go wild with them to provide the asked result.

And it's a prime "Let me show you the cool thing I made!" game. I made my youtube account only to share my creations :)

How about Impossible Creatures ?

Spore needs some creativity. You create your own creature then evolve it then create buildings and vehicles.

Oddworld series

It's a shame that the game didn't live up to what was promised before it was released :/ It's still a fun game, but it could have ended a lot better. They even got rid of some content shown in the demo.

Have a look at Don't Starve. I was completely caught unawares by the brilliance of this game. The creativity comes in with the setting up, expansion and maintenance of your base of operations. You can set up various farms, build defenses, and even automate some 'industries' somehow (with a lureplant or something). Its crazy fun too :D

Edit: You mentioned Evil Genius, and Licurg mentioned Dungeon Keeper. So these two also have to be mentioned:
Startopia (one word : Biodeck)
Theme Hospital (Its fun planning out rooms and getting the most out of limited space)
and also, from the 'tycoon' series:
Rollercoaster Tycoon 2 (inventing rides)
Transport Tycoon Deluxe (designing complex transport networks)

Edit2: I can think of one other recent title on gog that demands to be recognized in this thread, but I don't want to deny TinyE the pleasure of pointing it out :D

The sims i guess. You can do tons of stuff there if you don't mind spending like a billion dollars on all the dlcs.

Yes! this game makes you talk to those you want to save; you need to get their attention, not just randomly walk by.

If you can manage the difficulty, Dwarf Fortress reigns supreme.