I just find them very annoying and pointless. Wouldn't the person who started the QTE have an advantage anyway, since they know its about to start.
Hmhm ... alot of people are sick of QTEs, I think. Even though Guitar Hero and Rockband, the biggest QTE-games
ever, are that popular.
Anyway, I think QTEs are very useful if it comes to cinematic approaches in games; which a melee-combat-situation in a shooter definately would be.