two stand out for me
Mario64 on N64, my mate got a japanese import about 12 months before the uk release cost him £500 for the 64 and £99 for the game!!
I was blown away, it was like playing a cartoon, he set it up at about 6pm, at 5am(!!) we were still playing it
Star Wars:Knights Of The Old Republic on the X-box, the BEST Star Wars game ever, an Epic game lost months playing that!!
Still got it as its compatible with the 360. If anyone has a 360 get it!!, its really cheap (around 10-15 pounds) well worth it