cool game and fun to play, but could use some work. maybe having the same loud sound play everytime you hit something isn't the best idea? at least it got annoying to me.
The physics are also a little hard to control. Bouncing off the walls gets hard to estimate exactly where you are going to land, which leads to more deaths. speaking of, when you restart at a checkpoint, your timer resets. I'm pretty sure this is not intended, as that completely defeats the point of the timer. also I found the two buttons "restart" and "checkpoint" to be a little weird. restart should be below checkpoint on the menu.
The gunplay was good enough, I really liked the recoil with the shotgun, but I found it a little hard to shoot enemies, as there are almost no hit indicators or a crosshair/aiming visual at all. also I feel like you could have stuck to the theme a little more. i know when you hit the red you "overheat", but its the same basic function as most platformers, and there is nothing saying it is fire or lava or whatever.
besides all that, this game is still fun to play. good job, make sure to rate mine too!