I have found that most of the time they just suck and really take me out of an experience. I found this in both Force Unleashed and RE4. However, I find that quicktime events can be a way to immerse a player, if done right that is, such as the hallway sequence in MGS4, where the player's desperate pounding at the triangle button almost makes you feel Snake's suffering as he attempts to drag his almost lifeless body through the corridor. Then again, the ironic thing about that is that it only seemed to immerse you because you were feeling pain after frantically tapping that triangle button for well over a minute, so I guess that means QTEs are just painful any way you look at it.