The games see the player take control of a set of animated birds who are attempting to retrieve eggs that have been stolen by pigs. The thing is that the pigs can and do hide beneath, behind and in front of a variety of protective environments. The other thing is that the there are different birds that can be used to attack the pigs in different ways. Some explode, some are extremely big and heavy and some can fly backwards. It's up to the player to judge which trajectory and velocity to choose for the bird that is available to use at any one time, then let them loose on the pigs and their protective environments.
The two follow-ups, Seasons and Rio, bring a seasonal twist and content based around the animated film Rio to the Angry Birds franchise. This all adds up to a LOT of content. There's a good 100 hours of addictive content on offer, not to mention 19 exclusive levels!