id say the same thing as the people above... but you have to take in consideration that your art is slightly much more different then just copy paste and adjust a tint ... as long you have the illustrator files where you composed all the image parts your ok to go .. no matter how the image looks like .. you can make a a 100% clone look a like.. as long you made the graphics .. there are plenty of clones that does it exact way just main characters or some parts are a bit different .. and the developers of angry birds... wont bother to come after you... its peanuts for them ... they'l probably consider it ... free advertising .. cause in the end.. people will play their game since has more fame and versions ... however you might not be able to monetize ur game ... you have to read the terms and conditions of some specific people who made the game
instead of bothering with a rip off id probably use the same game logic and make a unique character set with a unique theme ... like ... Zeus and other gods.. miniaturized in the angry birds style ... and the story wold be .. the run for Olympus or smth ... dont know ... depends on ur imagination and budget for graphics ...
Publishers: Rovio Entertainment, Activision, LucasArts, Chillingo
Designers: Jaakko Iisalo, Markus Tuppurainen, Peter Urbanics
Developers: Rovio Entertainment, Chimera Entertainment, more