The first word that comes to mind when describing the gameplay is: FRUSTRATING.

I'm saying that in a good way, it's challenging, and if you fail, it's a skill issue. Progression is a bit slow, I've been playing for more than half an hour on several sessions combined (maybe even an hour) and I'm still stuck with the first 4 colors of atoms because buying enough Hydrogen atoms for the next prestige is very expensive (at the very least you'll need 32 and then you have to combine them all fast and without failing). And the instability of Helium will make you punch the screen.

So yeah, progress is super slow, the nice thing is that it has autosave so you can continue it any time. It's still a fun game to try.