From Kotaku (via Joystiq):
For [Patrice] Desilets, however, 2009 and the making of Assassin’s Creed II was a wild ride, one of nervousness and frustration, some far-flung trips, at least one bout of vertigo, the affirmation of one major addition to the game and the painful decision to make a few — possibly temporary — [...]

From GameTrailers:
Patrice Desilets discusses gameplay features and improvements with new gameplay.

Video Games | Assassin’s Creed II | GC 09: Creative Director Interview HD
XBox 360 | Playstation 3 | Nintendo Wii