Several major improvements in progression and other details make Creed 2 a huge leap forward from the first game.
Gameplay- The gameplay is essentially the same as the first game, with some different progression systems. All of the climbing and platforming and combat are still there. Counter kills are still incredibly satisfying and finding the tallest towers are still a thrill, even if the tallest one doesn't compete with the Cathedral in Acre from the first game. The main difference in the gameplay is that in order to progress, one does not have to do the same three things to gain enough information to assassinate. Instead, there is a main quest with side missions that are optional. The main quest will always lead you to assassination missions, with other exciting ones that help the story along the way. Side missions including killing guards, delivering letters, and other stock adventures. The problem of boring and sometimes frustrating repetition is still present in these, however. This is one area where they didn't improve much. So in summary, the gameplay is basically equivalent, with different cities and story, with a hugely improved progression system. There is one major difference in the gameplay, and that is stores and your city. You basically own a city, and in this city, you can upgrade stores, shops, and other main buildings. Doing this ups your income and discounts items bought in your city. You can buy tons of weapons, armor, and clothing items. This is incredibly awesome and puts the game over the A level. I haven't even mentioned exploring for glyphs, feathers, and exploring the 6 assassin's tombs to unlock Altair's armor. Overall, the gameplay is vastly improved, enough so to completely set this game apart from the first.
Graphics- The graphics have not been improved much since the first game, and they are beginning to show their age. Water looks nice, and character animations are smooth, but framerate and texture issues still bog the game down.
Sound- The sound is quite crisp, and the voice acting is a huge improvement over the first game. It is superb, and everything from the music to the sound of walking on rooftops is top quality.
Value- With the added city upgrading, weapons and items, unlockables, story, and side missions, Assassin's Creed 2 has a lot of value, at least in comparison to the first. However, because of it's repetitious gameplay, you might want to rent it first. I bought it, and while it is a great game with a lot of value, it might not have been worth 60 dollars.
This game is a great example of what a sequel should be. It adds many things, and most of them are significant enough to give recognition to. It is a fun game with tons of details to explore. Definitely worth checking out, even if you weren't crazy about the first game.