So, I just finished playing AC2.  As a big fan of story-driven games and of the franchises Half-Life and Assassin's Creed (among others, but these series' excel), Assassin's Creed 2 wins the achievement for Best. Ending. Ever.  Without spoiling it, something happens and I found myself saying "Oh. My. God.  You have to end this right there.  Do not do one more thing.  Roll the credits NOW."  And the credits rolled, and I laughed out loud.  It was brilliant.

If you're a fan of story-driven games like me, and you haven't played the AC series yet, do yourself a favour and go get them, and play them front to back.  You can ignore the side missions if you like.  You also don't really need to experience AC1 to get AC2, but there are definite story tie-ins that you would appreciate if you did, and there are characters that carry through.  In fact, well perhaps you should just play AC1 to really get the full effect of AC2's ending.