I realized it while playing the game, and to a greater extent after reading the article, but it's a very meticulous game. The amount of detail and thought into all the aspects of the game are top notch. I really respected the architecture of some of the more complicated levels in regards to all the little angles, small blocks scattered, combination of material types, etc. In my opinion it's what the game is centered around. The fluff - sounds, visual cues, appealing characters, would not stand on it's own merit without the excruciating detail put into the level design. If it takes half an hour to an hour to complete a level, it must be exponentially more to design the level.
Angry birds reminds me a lot of the gameplay and level design of Lode Runner for the Apple IIe. Simple concept, artistic levels that were pictures or boats or houses, and totally addictive gameplay.
Now all we need is a level editor for angry birds...
My current aspirations of real full time game development can be traced back to designing Lode Runner levels on my first computer, a Mac 512k. I used to design levels in MacPaint and pretend to play them, because I didn't know any better.
