I noticed a huge HUGE difference. It's actually quite easy to tell really and I wonder why you even have to ask. When I first placed Rainbow Six Vegas in HD I immediately felt sucked into the game. It sounds weird but after a year of playing that game and in fact all games in regular Standard Definition it was extremely noticable. I could visually tell it was better and I somehow got emotionally drawn into it. I felt like I was on the top part of a roller coaster and it just started to fall straight down. I am never going back. These days its hard to even go back now.