Gangs of London fails not only because of its dull missions, but because of the way they're put together.
One of the good things about the game is that there are several gangs to play as each with their own story (though their stories don't really go anywhere). So there are these gangs trying to take over London, and they're at war with each other, and they kill each other from time to time. Major yawn. Like I said, the story doesn't go anywhere.
The game tries to be open-world like Grand Theft Auto and such, but it fails miserably because the missions are put together as... missions. You select them at the menu. Free roam is a separate mode. Who wants it like that? And this is the major drawback of the game. The missions aren't put together right. The story, or lack of it, is told through Max Payne-like comic panels, with awful voice acting.
Gameplay, hmm... you have a lot of stealth missions which are awfully hard to get through because this game obviously wasn't designed as a stealth game. Combat is dull and frustrating. Mostly you fight with knives, standing in front of a person and mashing the X button. The animations are awful. In gun combat, you don't aim your gun, you aim your character. You have to stand directly in front of an enemy, target them and mash the X button. Like in melee combat, the animations are awful.
You can drive cars, but it's like driving on ice. There's no friction, no sound of engines, nothing at all. The brakes on every single car in this game seem to be broken because they are useless.
There is only one music track in the entire game, which is like the music when they put you on hold, only it's much worse, and the voice acting is awful. You'd think with gangs of so many cultures would have their accents, but no... the Talwar Brothers, for example, don't sound Pakistani at all, neither do the Traids sound Asian, and all characters speak American English. In a game set in England. Can you believe it?
There is not a single thing to like about this game. Stay away, or you are doomed. Doomed. Doomed doomed.