I loved the game! I've been playing for 30 minutes straight, it's super addictive, and I got to a 208 high score.
In my opinion the movement is fine as it is. I've seen other people say you should be able to move more freely, but I think the fact that you have to coordinate both vertical movement and rotation to get the atoms to hit where you want is genius, as it is that you have to mind the correct orientation and that both main mechanics (making and breaking bonds) can be both good and bad depending on *where* it happens.
It is a very challenging game. It gets very hard very fast, so you could tweak the number of atoms or their hitbox (maybe the clock?) to get a difficulty curve a little more smooth. I also found it pretty punishing when you get atoms where you don't want them, as they quickly bump into others and it gets more and more out of control. However, the game also lets you recover and start from scratch if you manage to break the right bonds in the middle of the chaos.
To be honest, this is the best game I've played in this jam to this point. I hope you get to the top 20!