Most definitely. Assassin's Creed 1 was amazing for the first couple of hours. Getting to your first city was incredible, and felt really adventurous and real. Unfortunately, it became repetitive really quickly, and you ended up doing the same Investigation missions over and over again just to get to the good stuff (Assassinations), which took a very small fragment of the whole experience.
Assassin's Creed II changed this completely. The mechanics were still familiar but fantastically more varied, with better combat and way more weapons and opportunities. The revamp of the mission system was vital to the franchises future, and worked wonderfully. And the setting... oh the setting. Renaissance Italy has been by far the greatest setting I've ever encountered in a game. I actually went to Europe this winter and visited both Florence and Venice. I thought of the game the whole time... it really captured their feel amazingly.
The narrative aspect was obviously greatly improved too. The story got way more engaging, and the characters felt much more real. Ezio's dashing initial personality matured very nicely, and every single secondary character (Leonardo, Borgia, etc) was very well developed. Even Desmond became interesting for a short while!
The best thing, however, was the charm and magic the whole experience had. The first time you climb a building (after a race with Federico), when you get to the top of a chapel and see Florence from above was one of the best moments in every game ever. Ezio's Family (a song from the soundtrack I very much urge you to listen too) sounding in the background while the Assassin's Creed logo showed was a great touch, but what really made it was the conversation between Ezio and his brother:
Federico:"It is a good life we live brother".
Ezio: "May it never change"
Federico. "And may it never change us".
Those words resonated with me for the rest of the game, because of course... Ezio's life changes quite quickly. As soon as this words sounded though, I knew I was in for a hell of a ride.