Mistake #1: This particular jump.
Turns out that a lot of players die right here. Heck, I have the metrics to prove it. This is sort of a difficult jump because you have to make it across a wide pit and then land in a very small space near the top of the screen. This jump started out a little easier, but it got harder when I compressed the vertical size of this level to deal with some camera problems. The real problem here, though, is the distance. It turns out that this is the first spot in the game where you are required to use second-order flying skills to reach the other side.
Just what is that skill? Well, it turns out that some players never realize that they can stay aloft for longer if they let momentum rather than fuel carry them forward. If you press the jump button and get your speed up in the air, you can release the jump button and stay aloft until gravity overtakes you and you begin to fall. At that point you can hit the jump button again to combat gravity and maintain your altitude. You can't do this forever because you'll eventually run out of fuel, but using this method you can jump much greater distances than if you just hold the jump button down constantly.
The real problem is that I never teach players how to fly that way explicitly. There is lots of tutorial levels designed to make sure you can fly, but it turns out that only the most basic flying skills are required to get passed those sections. This area is the first in which you cannot progress unless you've figured out how to use the more complex flight mechanics, and people get stuck here.
What can I do about it? Probably this area itself is fine; a better tutorial on this particular skill is probably in order.
Mistake #2: The Case of the Robot Spewing Spawner
When I made the robot spawners, I though it would be a funny easter egg if you could possess them. Part of the plan was to allow the possession orb to possess any machine, and I thought possessing the spawners would be a little hidden reward for users that experiment. The problem is, I added this functionality before we understood how the robot puzzles were going to work; in the final game, it's trivially easy to possess a spawner, and most users are confused rather than elated. Even worse, being able to possess a spawner sometimes gets in the way of possessing a robot, which is pretty annoying. I realized that this might be a problem before we released the game, but I left it alone because I thought it was funny. Now there are multiple videos about it. Pretty undeniable proof that I messed this up.
What should I do about it? I should probably turn the easter egg off or at least find a way to make it much harder to find.
Mistake #3: The impossible puzzle.
You have no idea how many people have e-mailed me about this puzzle. It's clearly the most difficult part of the game for a huge number of users.
In the first version of the game, this section was missing the red spikes due to a bug in the level data, which made this puzzle even more confusing. But even after fixing that, I continue to get several e-mails a day asking about this part.
If you don't want this puzzle spoiled for you, stop reading now.
OK, I warned you. The solution here is to use the Possession Orb to grab the robot and run him into the button. Pretty simple, I thought; the real challenge in this puzzle's original form was actually just maneuvering the Orb through the spikes before it dissipates (in an update I added a gem to this level, so the Orb survives for longer). But it turns out that users weren't even figuring out that they could use the Possession Orb here, even though they've seen this pattern several times in slightly different contexts earlier in the game.
I finally realized what the real failure is here: players don't realize that the Orb can fly. The tutorial says something like, "tilt the phone to control the orb," but if you never try tilting it up, you'll never learn that the Orb can fly. I think that players also forget that the Orb is in their arsenal, but they'd probably figure that out eventually. Not expecting it to be able to fly means that many don't even try it. This is a fundamental teaching failure on my part and makes this puzzle a whole lot harder than it was intended to be.
What can I do about it? Well, as a first step, the tutorial level should force you to send the ball up at some point. After that though, the game needs to reenforce the fact that the Orb can fly, so I'll probably need to modify some levels to encourage that behavior.
The great thing about this is, I can fix the problems and send out an update and see if my fixes were successful. And if not I'll try again. Traditional video games have never had this sort of ability to iterate interactively with the audience, and I'm really learning a lot from it.