Even though this might have been your first GameJam this is probably not your first game because it already looks pretty good complete and I don't want to think back to my own first GameJams. The graphics were well fit for the scope of the project and so were the sounds. After having found the first surprise party house, the goal of the game was clear and I managed to deliver 3 cakes on the first day and 6 & 7 on the next two days. The replayability was of course not so high but that is also nothing that you expect from a GameJam game but through the upgrades there was at least an incentive to try them out. In terms of valuable feedback I only have that it would have been nice to see 2 rows of houses (if they have balloons) when you run horizontally like when you do when you run horizontal. But otherwise I would say that you have probably learned a lot yourself and will come more prepared next time yourself and do even better.
Have a nice evening :=)