Very interesting building puzzle game. I can easily imagine this being released on mobiles. It's funny and such a great use of the theme. Just incredibly imaginative. I had a lot of fun playing this.
In terms of shortfalls, it does get difficult to keep track of all of the hazards, as they come so fast. Maybe show some indication of where most of the balloons were burst. Another issue is that solutions may tend to become very alike. Meaning that people playing separately will tend towards having quite similar constructions. It's also very trial and error based, which can be fun, but can also become rather frustrating.
Obviously, you'd have to improve the visuals, but I think you know that already.
You have a great game, but will grapple with quite a few design challenges.