What are the main differences between EXT and NTFS file systems?

NTFS and EXT3/4 have completely different internal workings to do the same tasks, with the latest versions of EXT being slightly faster. The only real user-visible differences are support for them amongst Operating Systems.

NTFS is Windows native, but has full support in Linux and read only support in OSX. However Linux cannot really repair filesystem damage on an NTFS drive

EXT3/4 are Linux native, and requires a third party driver to be read on Windows.