The objective of Kaboom! is to, well...blow stuff up. You are under attack by well-armed and not-so-polite enemies. You can erect walls to protect yourself, and lob all kinds of incendiary devices at your enemies. But they will be doing the same to you. If they destroy all of your walls and take you out, then it's Kaboom! You get the picture.
Note: Kaboom! 1.1 Update is the same as Kaboom 1.1, except for new (and better) rules, as well as a minor fix to one of the cards.