What do you mean by general purpose HRTF? Do you mean that the HRTF should match the player's head somehow? I haven't played Papa Sangre so I don't really know how well it works.
Sorry for the late responses. Yes, I'd imagine it should work better. In my case I don't tend to hear frontal direction in most binaural recordings. How would you create such a custom HRTF? Measuring somehow or should it be manually calibrated? Seems like a pretty interesting problem, I might do some experiments with this some day.
Exactly, many people cannot differentiate front/back and up/down with general purpose HRTF, something that is much better with a custom HRTF.
For basic experiments, put 2 small microphones into your ear canals, hit record, then go for a walk. The result will blow you away :-)
To record your custom HRTF, get an anechoic chamber, put 2 small microphones into your ear canals, then record impulse responses from all directions. Not quite as simple.