I loved this take on the typical gauntlet-style turn based battler! Having to balance your health and radiation was a neat mechanic and having new skills every time you beat an enemy added some nice flavour too, along with the scaling enemy HP to keep up the challenge. Some variety in enemies, attacks, etc would've been nice, but like you say, 3 days is short, so it's not the end of the world. The enemy attacks did feel unfair at times - sometimes they would deal only 50 damage, sometimes over 200 - although once I figured out that you could see their attacks and plan ahead that helped with that problem. Some of the battles did also seem to drag on for a while, especially later in the game, so decreasing the health or increasing attack would probably help make things feel a bit more fast paced there.
The art was great, too. The characters looked nice and their idle animations helped add a bit of life to the game as well. The UI was brilliant, and it did feel very polished - even more impressive for a game made in 3 days, so nice work there! I loved how the UI was in the game world too, with it being on ropes hanging from the ceiling. It was a small detail, but I liked it. The sound effects worked well too, especially on the UI, and the music also was a nice backing track - although it didn't loop for me, which was a slight problem.
With that all being said, I think it was an brilliant game for 72 hours! The gameplay, the graphics, it was all well thought out and well implemented, so you did a great job! Excellent work!