The best values on games were ones where I could do more than just play the game a lot to give me x hours of enjoyment per hour. Some examples:
GTA3: This would always get reactions from my relatives (mostly men) who are only familiar with games like Pong and Frogger. One time, an uncle of mine who is a psychologist tried the game for a few minutes, and he was just in hysterics, muttering how "twisted" the game was. Nevertheless, guess what I got from him as a Christmas present later that year... GTA: Vice City!
Gauntlet Legends (N64): I admit, I got this for $35 used, but its value to me was much greater. My father was always a fan of the Gauntlet series, but he said he grew out of it and didn't have time to play video games anymore. I saw this game at an arcade, and I figured he might like it. I was right, and we spent many nights playing until two in the morning. We hadn't spent such quality time together in a long time.
Super Smash Bros./Goldeneye (N64): My friends and I play mainly RPGs, so we don't play tons of group games, but for some reason, we picked up on SSB and Goldeneye real easily. I don't know exactly how long we've played those two games, but it was worth it just for the occasions to stay up the whole night playing games.