Artificially increasing difficulty. One of the prime examples of this most recently was in the Bonfire of the Vanities DLC for Assassin's Creed 2. The game basically does this: "Remember all those neat tricks we taught you to pull of stealth assassinations? Yeah? Well screw all that. You can't do any of them here. Oh, and you can't be spotted, but let's fill up your notoriety so the guards are hyper alert."
It was infuriating and not fun at all. The first time in the entire game I actually chose to use the pistol, as it was the only effective way to deal with most of the assassinations. Find a group of random idiots walking even remotely where you need to be, swing the camera wildly until the horrible lock-on targeting hits the target, and then floor him with a pistol shot.
Again, not fun.