A few thoughts, speaking as a physics professor who asks his relativity students to play both "Velocity Raptor" and "A Slower Speed of Light":

* Like many others here, I was a bit dismayed to see this implemented as a Java applet. Increasing security concerns have meant that I've been able to use fewer and fewer of those in my classes: it's just not reasonable to ask students to jump through those hoops anymore.

* When I look at the menu, it only goes up through level 7.

* I have made very little progress on level 8 (the one with the diffraction grating in the middle that's trying to get you to reach 2% transmission at about an 80 degree angle on each side). I have a general idea of what you want me to do, but I get so little visible transmission most of the time that it feels all but impossible to fine-tune my momentum or other aspects of my strategy. (Is there any way to increase the slit widths or number of slits or something to make that easier?)

* What exactly do the arrow keys do? Are you imposing a linear potential gradient across the whole screen for a short time? It's hard to judge "accuracy" when I'm not quite sure what I'm looking at. (That also means I'm not entirely sure how to teach it.)

* Along similar lines, do you have a sense of what exactly is leading to the visible interference effects during motion? (The ones that you point out can be guides as to which direction the wave is moving?) Maybe I ought to have a direct intuition for this! Is it purely an effect of reflections off of the walls, or would I see the same thing if I started with a Gaussian wave packet in a linear potential without any boundaries at all? (And if it's reflection related, why is it mostly showing the direction of primary motion rather than the direction of the reflections?) Some explanation for this might be nice in a teaching tool.

* Do you think you could allow the user to toggle the phase-rainbow mode on and off? (That's the mode that I would expect to always give an indication of the dominant momentum of the wave function.)

* The "collapse" mechanic is very helpful for game play, but might deserve some sort of explanation. In particular, I worry that it could train students to believe a critical misconception: that if the probability of a particular state becomes high enough, that state immediately becomes "true". Maybe that wouldn't turn out to be a serious concern, but I'm not certain that beginners are well-equipped to recognize which weird aspects of game play are supposed to reflect real physics and which are mere game enhancements. (The way collapse works here feels a lot like Copenhagen, but not quite, since it doesn't obey the Born probability rule.)

* It would allow for significantly richer strategy and game play if the player had a wider menu of potential functions to choose from. (For instance, what if the arrow keys continued to be linear potential functions and a mouse click provided a harmonic oscillator?)

* In your explanatory text, I'm not comfortable with your discussion of decoherence. I'm far from an expert on that subject, so I'm hesitant to try to offer specific corrections. But it feels off to me. (In particular, a single quantum particle bouncing off of strict potential energy walls should not be a manifestation of decoherence, because the particle's state isn't becoming entangled with the state of those walls in any way. I don't see any manifestation of decoherence in the game.)

In case you're interested, my current favorite intro level textbook on quantum mechanics is Tom Moore's "Six Ideas that Shaped Physics: Unit Q". It doesn't go as far as I'd like for a really thorough course (which is especially true in the recent 3rd edition, though the material that's still there is presented much more clearly), but as part of an introductory sequence it does a great job. Much like Townsend's fantastic Jr/Sr level text, Moore first introduces the "rules" of quantum mechanics in the context of two-state spin systems (in a slightly simplified version of Dirac's bra-ket notation), and only moves to wave functions once the fundamental concepts are established. (It doesn't manage to do a whole lot with time dependent position/momentum systems like the ones you're simulating, though.)