The instance is single faction specific; requiring at least 4 people in the instance at once. The instance is set into 3 main phases for each faction. The Assault on the Shield Generator. Storming the Base, and Launching escape ships.
The assault phase looks like it could have been the best part except its got some serious lag problems. Rebels get to fly snowspeeders a nd try taking down AT-AT walkers before they reach the generator. Take out 4 walkers, get a token. The most horrid part of the whole event for rebels is there is no towcable, kill the AT-ATs with the speeders guns

The second part is simple: imps enter the base, you gotta protect certain areas long enough for evac.
The third phase, rebels have to protect transports as they evac and imps have to destroy the evac transports. Pretty straight forward. Evac more ships, get more coin.
They added a few other items, like a taun taun and wampa kill collection, a few hidden clicky collections like the meteorite and frozen taun taun, and a malfunctioning droid collection. But the biggest addition is the "side" quest called Wampa Valley. An instance within an instance where you face off against a small horde of Wampa before taking on Unkajo, the skullcrushing level 95 tower of a boss. she drops the best loot and is one of the hardest to kill.
Overall I gave the instance 4 outta 5 stars for the excitement and gameplay. The lag in phase 1 makes it meh aand no tow cables ruins canon.