You'll get more than what you paid for this game.
Assassin's Creed combines the best of stealth and action, delivering a super experience of how people used to act during the late 1100s. In the beginning, your character is a greedy bastard who doesn't care about anyone but himself, so his master makes him his student and takes away all his skills and weapons, which you will slowly earn back throughout the game. You can scale buildings, jump the Leap of Faith from the highest tower and assassinate, interrogate, pickpocket or punch any guard you want. The part that i had fun with is when you get your knife-throwing skills and through knives at the guards... it makes a relaxing sound as the knife penetrates the flesh.
Playing through Assassin's Creed, you'll find that getting to the first 2 leaders will be a load of fun. But after that, it gets repetitive... BORING! You'll feel you've done this before and you won't feel like finishing off those other leaders unless you finished ever other game you have.
A great feature they could have added would be challenges, like the ones the informers give you during the game for information. Like when you finish the game and you still want the Assassin's Creed experience, you can play challenges that unlock certain things that you can use to unlock more challenges.
Sadly, a game as good as this doesn't offer any online/downloadable features. If would have been great assassinating players online.
In conclusion, if you're bored and looking for a cool middle-age assassinating game, Assassin's Creed is the game for you.