The only MAJOR difference was the primary game mechanic; the projectile. CtC used a two tap mechanism where you launched balls from a trebuchet, it was all about timing. One tap to drop the weight, a second tap to release the ball. Progress through the game, you get three balls (yellow birds). Progress further, get bombs (black birds).
Suddenly, this Angry Birds game comes out, and the most noticeable difference is that it's cuter, and uses a slingshot instead of a trebuchet. A quick google search of the two brings up "Crush the Castle, Angry Birds set in midevil times".