Whats the difference between gpg and gpg2?

Currently using cygwin and have manage to compile gpg and gpg2 with camellia ciphers.  I might be slow, but I dont really see a big difference between gpg and gpg2.  Can someone give me a quick rundown about the difference between the two?  All I can see is that I can't compile gpg2 with the idea cipher whereas with gpg this module can be compiled in.  I'd be happy to provide instructions how to compile gpg with the camellia and idea ciphers if anyone is interested.