Angry Birds (video game) crates and rocks are incorporated into the structures, and power-ups may be used to enhance the birds to attack hard-to-reach pigs. Also in the levels, players can unlock bonus levels by collecting golden eggs. There are several different types of birds used in the game, distinguished by their color and shape. In the earliest levels only the basic red bird is available. As the player advances through the game additional types of birds become available. Some birds are effective against particular materials, and some have special abilities that may be activated by the player while the bird is airborne. For
Angry Birds (video game) called the game "an addictive, clever, and challenging puzzler", and "Pocket Gamer's" Keith Andrew said "Angry Birds" is "a nugget of puzzling purity dished out with relish aplenty". Jonathan Liu of Wired News wrote that "going for the maximum number of stars certainly adds a lot of replay value to a fairly extensive game". Reviews for the first versions of the game that did not use a touch-screen, the PlayStation 3/PSP version and the Windows version, have also been positive, but with some disagreement over the different interfaces. Will Greenwald of "PC Magazine", in his review of the PlayStation Network