I really like the setting of the game - fifteenth century Italy - and the nonlinear gameplay. Nothing forces you to play the main story right away as there are ample side quests that you can tackle first or in between. Graphics and sound are also top, as are the animations (especially when fighting/assassinating someone or freeclimbing up buildings). What I didn't like is the fact that I finished the game in less than a week - and that's not with playing around the clock but with a couple of hours in the evening most days. They already have such elaborately built city models for Florence, Venice and others - why not utilize them in more quests? There are two downloadable extensions until now, we'll see how long it takes to play them.
Overall I would say the game is worth the on sale price but if I would have paid the full price I would be disappointed by the short time for playing it.