The game looks decent but it would look much better if the buttons were custom instead of the default and if you mixed up the font style. For the actual games themselves, I will review all of them and give you feedback.
Madness zombie survival: Lacks variety. The same zombies come at you and their spawn rate increases over time. No powerups, no different zombies, it gets boring very quick. I would recommend adding powerups, make some different zombie types and instead of making the background changeable by the player make it automatically change when you get to a certain score threshold. (especially since later on its practically impossible to change it without dying anyway.)
Madness arena: Easily the best of the bunch. Sadly it also gets very boring very fast. The lack of a goal made me lose interest in about two minutes and the enemies all feel the same and do not make you change your playstyle whatsoever to defeat them.
Hominid homicide: kept me entertained for the longest time (5 minutes) but its also a little bland. some more enemies would be cool. You should nerf abducting because its op and makes you practically invincible.
Rammy's run is the worst out of the singleplayer games. It is slow, and boring. The reason games like flappy bird were so popular is because they started out very hard and got even harder which made you wanna keep trying to get a new high score. In this case it starts easy and barely gets harder.
I could never find anyone to play the multiplayer games with so I cannot provide any feedback for those.
The cinema is okay. Not much to say about it.
So is the claw machine, nothing to say there.
Same with coin pusher and double or nothing. Though I do kind of wish there were more original games I am satisfied with the amount that are currently in the game.
That is all I have to say. Thank you.
EDIT: On the madness arena part where you said you might add bosses, I think an easier and more effective way to do this is change the way you defeat some base enemies. Such as make some more powerful enemies have these helmets that you need to shoot off before you can damage their head, or make flying enemies that drop slowly moving projectiles from above. It would make the player need to scan the crowd of enemies to quickly make a strategy on how to deal with them rather than holding down left click and hoping for the best.