The main difference between the newly released Xbox 360 and PlayStation 3 versions of Assassin's Creed Brotherhood is that the PS3 version has eight "exclusive" missions. I played them last night to see if this is a difference with significance.
The free downloadable missions involve Nicolaus Copernicus, the newest historical figure to be woven into Assassin's series lore. He is the great astronomer, the man who defied the Catholic Church by positing that the Earth revolves around the sun and not the other way around.
Unfortunately, Copernicus, like Machiavelli in Assassin's Creed II, inspires no new gameplay and no great missions. The eight missions feature some assassinations you must commit under time pressures and a few skirmishes against waves of soldiers, but nothing in the Copernicus add-on is revolutionary, pun intended. They are the weakest part of the otherwise-fantastic Assassin's Creed Brotherhood.
I've captured the entire first mission here so you can see for yourself. I accessed it through the game's series-new mission replay feature. That should explain the clipped ending, since the replay mode doesn't slide you into the second Copernicus mission, which immediately follows. (Warning: I'm using my fully-leveled character here, though I don't think you'll see any spoilers.)
Completionists might like having access to the missions. It's fun to see our hero assassin Ezio interact with another historical figure. But the Ubisoft developers working on this series, for all their excellence, are beginning to develop a pattern. While they have been able to make fantastic missions in this series involving Leonardo Da Vinci and some of Renaissance Italy's great scoundrels, some of their personality-centric DLC, such as the Machiavelli Bonfire of the Vanities released for ACII and this free Copernicus pack here do not fulfill the promise of including such interesting historical figures. Machiavelli's DLC barely addressed the assumed master-planning with which he is associated; Copernicus' has little to do with science or astronomy.
The best free Assassin's Creed DLC remains the unlockable Uplay secret location for ACII. That expanded the lore of the series significantly. Copernicus' adventures are missable, less interesting than most of the missions that ship on the Assassin's Creed Brotherhood disc.
I wasn't able to find out yet whether these missions are exclusive to the PS3 forever, but Ubisoft eventually sold all of its ACII DLC to all of its console consumers. There's a decent chance the same thing will happen here.
And for one more look, here's the first part of the seventh Copernicus mission. Admire my moves!