While you can disassemble or decompile the executable code, you cannot get the source code, because certain information like variable names, structures, function declarations is lost, non-existant in the compiled code, since it's not necessary to run the code.
The games often require a high performance, which can be only achieved if the code is executed directly by the processor (CPU),
For this reason Rockstar Games makes their games in C++ language, which can compiled to direct ASM code, with the appropriate compiler for selected platform.
Games for Android like Bully or GTA are a combination of little Java code + resources (classes.dex) to handle the interface and the library, made from C++ code, compiled with the Android NDK.
Analogously the game for iOS is also made with the C++ code and the library is created with the use of compiler.
The best disassembler in the world appears to be IDA Pro.
I have made certain scripts that can create a new .apk archive.
