Obsidian

Real-time:
*) capturing the tornado
	- simple-minded and annoying
*) the lightning tree
	- I lucked out and solved it with just a few random clicks, without
	- knowing what I was trying to accomplish. Tried it later and gave up:
	- it's very tedious.
*) crossover switch (endgame)
	- a perceptual puzzle: you don't have to move quickly, but you must see
	- and remember the details of a quick animation
*) deciding to end the world
	- You have 5 seconds to decide whether to let Ceres implement her own
	- paradise or to destroy her. It not a puzzle, just a selection of which
	- ending cut-scene you want to see.

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Relevance:
The challenges are dressed up to fit into the world of Obsidian. At heart,
though, many are abstract logic puzzles, with a few real-time challenges
thrown in. There are a few that fit in well with the story:
*) the filing system
*) the card-cubicle runaround
*) mixing chemicals
*) programming the church robot

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Difficulty:
Overcoming the challenges tended to be easy, although occasionally tedious.
Figuring out the goal of the challenges was the hard part.
*) programming the robot
	- you have to figure out that the robot is dynamically reprogrammable,
	- then you have to work out how to do it
*) turning out the light
	- maybe it's just me, but I thought it was a clever lateral thinking
	- exercise
*) the tanagram
	- the clue for the goal of this is cleverly obfuscated
*) mixing the chemicals: figuring out the rules
	- easy once you've learned Obsidian's laws of chemistry