I think we should define "creative" a bit better.
Seems like diego is also referring to creativity that's asked of the player.
I'd say that's really hard to reach in an adventure game as opposed to e.g. an open world game or something like scribblenauts.
If you have a really complex logic or mechanical puzzle where you can find your very only formula and way to figure it out I'd say you could call that creative in a way.
But basically in an adventure game you are following a given path or choose between given paths. In almost any modern shooter or rpg you can be more creative than in an adventure game meaning you can follow paths that weren't intended or planned by the developers, find exploits etc. AI (artificial intelligence) is something one can have a lot of fun with.
Adventures generally lack AI. And thus fun. (Just kidding.)
But come to think of it, you can be more creative in Doom 1 of the early 90ies with its very crude and downright stupid AI than in any game in the top 10 of the Adenture Gamers Top100. Probably except Portal2.
The goal is set and the method, but the ways are unlimited.
Perhaps what diego means is for the part of the player better described as the opposite of spoonfed. (Help me out here, I really couldn't come up with a better term right now.
It's not autonomy. It comes down to "work", even if it's fun. Perhaps knowledge in some instances.)
For the part of the designer I think we are in the same boat when talking about creativity or as diego also called it: "originality"
I have many gripes with Telltale's games but I'll have to agree with Iznogood on that: They have by far the most creative puzzles today from what I've seen. Tales of Monkey Island had some very dull and horribly repetitive ones, but some were excellent. (I know I was especially delighted with 3 or 4, even if I can't remember them exactly. Every game has a high replay value for me nowadays.
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