The Battle of Forli gives you more AC2, but at the expense of the game's high quality.
The Battle of Forli fills in Sequence 12 (one of two "corrupted" memories from AC2). However, this sequence is extremely short and leaves you on another cliffhanger to encourage buyers to spend the $5.00 on the following DLC that finishes filling in the gap.
Let me start with the positives of the DLC. We actually get to see Caterina Sforza shine in what should have been a bigger role in the main game to begin with. The flirty back-and-forth between her and Ezio is entertaining and her brashness is truly humorous to watch. This DLC pack also gives you the opportunity to spend more time in Forli, which unless you spent time collecting feathers and treasures, you probably spent no more than ten minutes in during your play-through in the main story.
That being said, though, the shortcomings of this DLC pack are numerous. Much of the short sequence is spent in large scale battles and protecting those you are escorting. The story really is quite small and straightforward, leaving you bored and uninterested. It makes you wonder why Ubisoft would release this on its own rather than with Sequence 13.
There is only about one hour of extra play time added which is a huge disappointment for those looking to fill in the gaps and spend more time as Ezio. There is little variance in the few tasks you have to do for the story and the amount of traversing you have to do in Forli gets old due to the sweeping, water-covered ranges and high walls that often force you to run around the whole perimeter of Forli before you can get back in.
Honestly, if you enjoyed AC2, I would recommend purchasing this with the next DLC content and just play through both together. It is such a short, unrewarding experience, but for $3.99 you get to fill in more of the story which is welcome in the eyes of someone that really loved AC2. There is some humor added to the sequence that does lighten things up and make you happy you downloaded it but you have to wonder why Ubisoft couldn't have spent more time and energy making this sequence just as immersive and entertaining as the other sequences.
The Battle of Forli just lacks some of that classic AC inspiration that would have made it more entertaining. You still get to sneak and kill which really didn't get old in the game, and it surely won't be old after this one-hour add-on. I think it's worth it just to get some more Caterina Sforza and to see the hilarious consequences of having killed a monk earlier on the main game. If you are on the fence about this purchase, buy it and try to enjoy the few extra precious minutes as Ezio.