This game is great it does give the vibes of buckshot roulette in a new very interesting way. For new features I would suggest these things:
1.-You could add an endless mode where after you beat a test subject another after another comes next, and to give a buckshot roulette vibe you could ask if you want to continue or leave but in this way.
Assuming that you a re a drug addict, you could show a psychedelic pill as the continue and a boring color pill for the leave. For an extra, if you choose to continue, you could add a brief psychedelic effect to the screen showing how desperate you are for the feeling that the drug gives you for an instant.
2.-For the game mechanics, you could configure that the secuence of the pill is not always the same, and also that the type of pill not necessarily defines what the pill does, I mean, that not always the blue pills Regen 2 points of tolerance and that it can do other pills effects, and the same for the other pills.
3.-It could be great if you add a multiplayer mode for at least from 2 to 4 players.
4.- I know you said that the AI of the other test subject sometimes fail but you can improve it.
5.-for the picking up of the objects you could make random the amount of items you can pick up per round and not always only 2 objects.
6.-There are occasions when there are only killer pills, when this happens you could add heavy breathing and laughing expressions for the other test subject, and if the other test subject knows he is about to swallow a killer pill you could add fear to his expressions.
I know that maybe I ask much but I really liked the game and I got excited with all this ideas jaja, good job and congrats for the game