When I first brought Assassins Creed I was really put off the game for the same reason that most people have expressed their disappointment in this game. The prospect of planning out an assassination by collecting information through eaves dropping, intimidating and pick-pocketing sounded great and the first time you did these things was really awesome. But then repetition sunk in.
The problem with this game is once you have played one level you have pretty much done everything this game has to offer. The different investigations which make up the majority of the game are the same in every city each time you carry out an assassination.
It was after I initially traded the game in that I began to look back at it more favorably. In my opinion this is a really great game that you should play in moderation. Playing the game through in the space of a week left the game looking mind blowingly dull. But now I pick it up every now and then and each time I always really enjoy my time with it.
The actual gameplay is absolutely brilliant. The way you climb up buildings and leap around each of them is enjoyable and performing assassinations on unsuspecting guards and Templers is also a great pass-time. The combat is a little clumsy but OK and the story is really interesting.
If you haven't played it yet I recommend it especially as it is much cheaper now and if like me you traded it away, give it another chance.