They added unit veterancy,
fog of war
the AI is different
a new UI
new network code
you can switch between high res and pixel doubling on the fly
you can change the stance of units (defensive, fire at anything, do not fire, etc)
you can queue production of more units and buildings
Frankly all of the changes seem positive to me, just basic shit to keep it playable today.
There are still a TON more people playing on that other network with the original games though, this just looks superior to me, and is still being developed