I've tested it on a real CoCo 2 (PAL) and, wow, is this game hard! I've made it to level 4 now.
Using a non-self-centring joystick is mega-tough. Diagonals are very awkward, you spend a lot of time stuck against the wall while trying to move the joystick to a useful position. You can't fire while "stuck", which makes it even harder.
Self-centring joysticks are a
LOT better. I don't know if it's my imagination, my joystick, or whatever, but I feel that I have to push up slightly further than I have to push down to move the player?
Real digital joysticks (using an adaptor) are top notch.
Keyboard controls take a lot to get used to, but that is basically unavoidable.
Erm... you could release it on a special cartridge with 4 digital joystick ports?
If you follow behind a baddie, you lose energy even if you aren't that close.
When I got to level 2, using only player 4, I couldn't walk into one of the (supposedly) empty squares that one of the other players would have been in, had they been selected (the top right one). When I shot at the empty square, the non-existent player lost energy until they died. At that point the bones appeared and I could walk over the square again.
Ah, I just see you've release beta 2! All my comments are about beta 1.
I see you've tried a Megadrive pad on one of the Atari adaptors. It doesn't work too well. My Altai adaptor always has the joystick off-centre when I try a Megadrive pad. That said, I believe there is someone in the C64 scene who sells an adaptor to use Megadrive pads on the C64, as the extra pin connections can cause diabolical problems to the C64, so maybe they could be used in concert with the Atari adaptors?
=======================================================================
Edit: A short update about beta 2.
The level 2 "empty square" bug is gone, joystick sensitivity is OK (although non-centring joysticks are still terrible).
I haven't played it as long, but I can't find too much to fault. The only thing I can think of is that the left joystick fire button sets "N" for NTSC on the CoCo.