Even though the first two missions are the same as in the retail version, the loading screens are completely different.
The scene is set for Thrall's adventure: his fleet of commandeered Alliance ships has to seek refuge from the storm on an unknown island.
That Troll provides a side-quest involving a search for some ingredients so that Sen'Jin can purify the defiled Fountain of Health.
Quest completed, and you also get a little reward (besides being able to heal your units near the fountain) - healing wards Thrall can carry around.
In the dungeon level, both Orcs and Alliance troops are prisoners trying to escape. Still have to battle each other though.