I liked it a lot! It has really good graphics, the animations of the furnace (when attacking, or the feedback when you hit him) feel very good and the smoothness of the gameplay is perfect. The mechanic of poisoning yourself to make the gameplay harder is super original and gives you freedom to fit your playstyle. I love the ground effect when the furnace smashes the ground, and i like the little detail when your bullet hits the furnace's shell :). I set my record on 26 heat and 30 seconds. Very good work! By far one of the most challenging games that I have enjoyed the most on Itch.io :D
Small feedback (I know the game was made on a Jam so everything is not possible but here it is): A soundtrack would have been incredibly good to the game and refering to the gameplay feeling, I would have added a bit of weapon sway and camera shake!