Clever mechanics! I was missing a bit of urgency when placing the blocks, but a super unique entry that fits very well with the theme!
Viewing post in Stick the Brick jam comments
Yes, the sfx and music could definitely help. I did see the bonus countdown, but somehow it didn't feel very 'real', if that means something? Maybe if you also added some kind of negative effect (e.g. spawning random blocks or similar) that happen in the main game? This might be just me but in these kind of games i always end up focusing fully on the main mechanics and don't pay attention to the HUD :P