The Trophy is the very first block which lets players complete a world. Once he or she touches it, they complete the world. Upon touching it, the screen will say that the player has completed the world and you can choose to go back to the Lobby to play a different level, choose to stay in the same world he or she are currently in, and/or give the completed level a Woot. (Now Woots are gone and replaced by likes and favourites, now you can't goto lobby instantly when winning a world, because this is campanign only)
The Trophy was exciting to users at first because it was the very first time someone can actually win the world. Before the Trophy came out, people used the crowns to win the game, but now they will get noticed for winning a world.