What are the differences between unhybridized and hybridized orbitals?

An excellent example of this is Carbon. In the ground state the electron configuration of Carbon is #1s^2 2s^2 2p^2. The four valance electrons of Carbon in the ground state are in one filled orbital the 2s and two half filled orbitals the 2p The Lewis dot structure looks like this
.
: C .

This structure only allows Carbon to form two bonds as in Carbon Monoxide CO
. .
: C:: O:

This structure is not completely stable as Carbon has not achieved the stable structure of Helium with only the #1s^2#

By moving one of the 2s electrons into the empty 2p orbital Carbon now has four electrons that can be used for bonding. There are now four equal orbitals 4 # sp^3# orbitals. The s electron that has been moved into higher energy level than the ground state.

The new electron dot structure looks like this.
.
. C.
.

This new structure allows Carbon to bond with two Oxygen as in Carbon Dioxide
.. ..
:O::C::O:

This structure is completely stable as the Carbon can now have be considered to have either eight electrons in it outer shell like Neon.
or no electron in the second shell like Helium.

By moving an electron from the unhybidized ground state to an higher energy hybridized state the atom is better able to achieve a stable electron structure.