It had it all to be a great game, but it's flaws in plot and gameplay made it not worth the serie's legacy.
I would have waited another year, if that time would have turned the game in something as good as AC: Revelations. I would have gladly waited two if that meant AC3 would be as good, if not better, than ACII. But it is today, and ACIII is not any of it's predecessors.
I haven't been so disappointed with something since I saw Dark Knight Rises in a theater, and before that, so long I can't remember. While ACIII had absolutely everything to be an outstanding game, Ubisoft's hurry into making the game fit in time to the announced end of the world resulted in it coming out with unforgivable flaws:
First the script is just horrendous. With giant holes into the story, some sort of lack of motivation of characters, the whole thing is worth a low-budget movie. Connor, the character, is just unrelatable and very annoying, to the point that made me wish out loud I was playing with Ezio. Connor does not just act like and idiot, as he does not change or become wise. He's just a kid playing assassin and not growing up. I was way more satisfied when playing with his father, Haytham, and he is a Templar nonetheless.
Then there's gameplay: It should be awesome, but it just looked like it was finished in a hurry, cause there is so many bugs and lags and textures that do not load, animals stuck into trees and Connor not obeying the commands, simple things that could be solved with maybe six months more of testing and reprogramming. The combat system was made easier and dumber, but still works, for enemies are more suited. There are improvements, yes, but I would take ACII anytime with no doubt.
And, if all that is not enough, the present parts are just horrendous. Clearly somebody messed it up really really bad. The locations do not make sense, the missions are pointless, the characterization of places and people couldn't be worse (as a brazilian, I don't know if I was more horrified by the characterization of our country and the bad spelling of language, or the fact that the UFC fighters are fighting in pants and shirts). The enemies are dumd, the weapon system for them does not work, and the plot here is far (oh, so far) worse than the rest and, for what counts, anything worth be named ACIII. Of course, the ending made me want to play next, and the themes are good, but the solutions are poor, the twists are predictable and, most importantly: it has no meaning at all. Nothing is explained, but things in the present solve themselves so poorly that made me sick.
I think people should play it. It has a lot of good moments, and it is, indeed, fun, but it is so beyond anything that was announced and any expectations set high by it's prequels, that made it the most disappointing game I've ever played. Not because it is bad, but because I've been waiting for a ten.
I have not tried multiplayer yet, and maybe I will be more satisfied with it.
As long as the single player and story experience, I hope the sequel learn from ACIII's mistakes, and Ubisoft delivers a great game, worth of the burden of being the new and best Assassins Creed, for this is clearly not.