It's the new stuff that everyone likes
All aboard the S.S. Bandwagon!
Also, I believe the reason most people like it is because you have to actually consider what throwing a specific bird at a different block will do, and whether or not it will maximize your chances of success.. Like, you have to consider "Hmm, do I use the White Bird to take out the middle, and collapse the center of the building, or use it to destroy some of the foundation, and topple a fair amount of the building?" You also have to consider the proper trajectory, exactly when to use a specific ability, and how exactly to take out the pigs' fortress.
It's a game about tactics, really.