It is not that bad when you thinki about it. Consider people who play COD4(I did). You play the same maps, matches and usually use the same gun. Many games are the same thing over and over wether singleplayer or multiplayer. All that matters is the experience you take from it. Personally I love Assassin's Creed and do not mind the repition at all.
Whats so bad about flag colelcting with a time limit? it is so easy its ridiculus, if you actually failed it then you mustnt be very good at this game. just because you didnt find it fun doesnt make it the worst game in the world.