Whilst it opens up a new area in Florence, the area is somewhat void of activities.
So the Bonfire of the Vanities fills in the gaps of Ezio's memory sequence number 13. The events took place right after sequence 12 (another part of Ezio's corrupted memory sequence – aka DLC 1) as now Florence is under the rule of the monk Girolamo Savonarola – the chap who stole the Apple of Eden from Ezio. Naturally he uses the apple to subjugate the populous and ruled the city with nine lieutenants. So you being the assassin is to get rid of this evil and bring Florence back into order.
Because you need to assassinate every folk, it brings back to the roots of Assassin Creed 1 (Altair assassinating nine high level Templers). A coincidence I'm not sure however the game ensures that you cannot simply barge in and kill everyone on sight. That's a good thing in my eyes as I tend to do this and frankly, it does make things easier...well for me as I love that counter attack move.
So there are different variations to assassinate your targets – some do require to barge in, similar to I guess like 'Hulk Smash' however some do require blending thus assassinate whilst not being detected. Some are quite easy however some are challenging indeed; especially the one on the boat where he's surrounded by guards of all types. This places variations to your approach and it kind of reminds me of doing those mini assassination quests – the ones you get from the pigeon in the cage.
Beyond that, this DLC also added three templar lairs where it plays very similar to navigating those assassin's tombs (the ones where you need to locate the seals). Besides traversing these tombs reminds me so much like Tomb Raider (but that's another story), knocking off those templar tombs plays just that however the end result is earning a bucket load of florins. Yet by that stage you really didn't need any more (well one hope so) however still entertaining enough to take advantage of that 'free running' experience.
Considering the main drawcard was an opening of an entire new area, sadly there are no treasures to be found (as I was hoping to buy a map from the merchant and alias there wasn't any). I really don't give a rats about earning more florins however it was fun locating them. Of course there's also no codex to discover and no mini assassination quests. So the entire area is pretty much void of side quests, which is a total shame. It looks like they wanted this area to be in the main game however for some reason didn't; so no side quests for you.
I'm not sure of the expected completion time however I knocked it off around the four to five hours mark as practically there's nothing really to do other than assassinate. This is not a bad thing however I did expect to have some additional side quests or even additional treasures to find; yet the three templar tombs, even though they all felt like traversing the assassin's tombs, beyond that there's nothing much else to go for. So if you are a completionist (like me) then go for it however, and thankfully so, it's now included in the deluxe edition, otherwise it would feel like a rip off if I have to fork extra cash for it.