Cool little game. The click and drag mechanic seemed a bit unresponsive (Is your input code in FixedUpdate by any chance?)
The trucks are pretty slow to come in after leaving (At least initially, I didn't get super far) so there's moments where you're just waiting for trucks to show up.
It'd be good if the randomness was dialed back a bit so that you don't end up in scenarios where the shape you need doesn't appear for a while. You could just spawn the shape in if it doesn't appear after x spawns.