Add screen wrap for parts of the arena which are both under one player's control- the player and their shots could wrap. This would be really cool. As an option, probably.
All the collision was handwritten (compared to using Box2d or something) to actually assist in doing this properly with the players. By properly, I mean having a player be able to exist 60% on one side and 40% on the other rather than just teleporting over as most games do. That said, I've never actually sat down and implemented it. I think it would need some sort of border drawn around the playable space such that you can differentiate between the wrapping tiles. This might actually help in communication when there are holes in the center of the levels anyways.
Add an option to disable the fast shots spawning- an alternative would be giving players fast shots in certain intervals but have the interval increase/decrease based on how much of the screen they own?
For the majority of development, there were actually no pickups. I just added those a few days before posting on here. I really liked the purity of it, but the lack of engagement while out of bullets was the most common criticism. On one hand, you want to punish the player for going all out in attack, but having nothing to aspire to other than the passage of time as bullets reload was an issue. I tried a few solutions (active reload type stuff, etc) but nothing stuck until the pickups.
I could certainly see disabling them in an alternate "pure" game mode. What exactly prompted your desire to play without them?
Rebindable keys for players one and two at least (I couldn't figure out which keys control player 2)
There are no keys to controller player 2. The keyboard controls are mostly just in there to assist with development. It lets me test the basics without a controller plugged in. The keyboard player is at such a disadvantage without analogue movement that adding more keyboard support hasn't been a priority. I could perhaps see keyboard vs keyboard being fair and I'm sure I could add some more acceleration to the keyboard inputs to allow for extra precision.
Did you get to play with controllers? Also, how many players? And did you end up having keyboard vs controller games?
Replays
That would definitely be cool. It's on my long term TODO list for the codebase.
Charging and releasing while holding two keys could shot one shot between the two directions instead of three in one direction maybe? I feel like a little diagonal action would be cool.
I agree that rewarding complex inputs (similar to a fighting game) is an interesting avenue. I'd be a little concerned that diagonals would be hard for a player to predict which cells will be flipped. Perhaps some sort of stair-step pattern could solve that... I've never actually considered the split two directions. I suppose that it could help you in spatial control and blocking the opposition in.
Thanks for the feedback!