(1) Too CPU intensive: Around 60-70% CPU. It slowed my gameplay down to a crawl, and made my PC slow responding. Sometimes I would end up GAME OVER from freezing before I could even move.
(2) Add difficulty levels (slow down how fast heat drops, etc) and maybe a sandbox mode to be able to experiment -- Especially with the high CPU issue! The farthest I have gotten was to build a smelter, and was just about to build a furnace. Then, a mis-click sent the wrong materials to the wrong place, and the CPU load made it take several seconds for my corrective actions to register in the game. By then, I froze.