Very, VERY overrated
But is it good? NO
The objective of this "game" is to throw different types of birds to kill pigs. Right now, there are about 7 types of birds in this game, each having their own abilities. The problem however, is that there's numerous FREE flash games that are similar to this $1 game, like Crush the Castle. There's tons of levels to play, with more levels getting added via updates. It's not like you would finish all of these though, you might get bored after a few levels.
Another bad thing about Angry Birds is how Rovio releases more Angry Birds games just for new levels. There's nothing wrong with adding the Seasons and Rio levels in the main game, but the're still releasing them as standalone games.
Overall, this game sucks. It's just sad that people nowadays prefer casual games nowadays, and how people actually choose the iPhone over dedicated gaming handhelds, just for trash like this game.