6. All Of Deus Ex: Human Revolution's Bosses
Why oh why, oh why did Eidos choose to outsource development of their boss battles to another studio, whilst they kept the focus of a sci-fi action RPG flowing throughout the main game? We'll never know, but the end result was a game that had laser focus on making you a cyberpunk badass dabbling in everything from stealth infiltration to duck n' cover gun battles 80% of the time - only to come up against bosses that demanded a particular playstyle beforehand. They were all rolled out this way, but especially first encounter Barrett, who elected to lob explosives at you whilst continually walking your way and closing the gap, meaning if you'd previously dedicated yourself to playing stealthily, there was literally no way to do damage unless you happened to have enough ammunition left over.