The GemCraft thoughts come from trying to ride the bleeding edge of difficulty. Sometimes we look for greater challenge because easy is boring, but the leveling system in GemCraft also encourages you to push yourself as hard as you can. You cannot grind the same map repeatedly to level up. Instead, your experience point total is the sum of your highest score on each map. You can go back and repeat a level, but unless you up the difficulty and therefore your score, it will not contribute to progress.
So add more difficulty modifiers, add more waves, boost the waves, and summon them early: anything to up your score, because if you go easy this time, you’re probably coming back to re-do the level for a higher score (for more levels, to do better in the late game). And who wants to re-do 40 waves of defense when you don’t have to? Only now you’ve dialed it up to 50 waves and are trying to keep boosting that difficulty mid-level, eek out a little more and keep things interesting. Of course, if you overshoot the difficulty, you’ll probably find out all at once, and now you’re starting those 50 levels over. I have several times ended levels because I boosted several waves of difficulty without noticing their different speeds, so they all reached the critical point at the exact same time. Hurts.
GemCraft: Chasing Shadows also comes with “Iron Wizard Mode.” No xp, no levels, no shadow cores, no talismans, no difficulty dials: just 5 skill points per completed map and that is your total advancement. There is no way to lower your difficulty by re-completing levels with higher difficulty. There is no benefit to increasing your difficulty, unless making one part of a map harder makes another part easier. There is no bonus for completing the level quickly, well, or with perfect defense: just win at all. This is remarkably freeing. Making the whole thing pass/fail takes a lot of pressure off, even if the fixed difficulty can be a challenge to re-adapt to after having lots of levels in the main game. Also, I am now seeing the first levels again, with their few waves, rather than the 50+ wave maps I am seeing 80+ maps in. The simpler game is soothing. I can choose to have fewer choices.