For me, Spyro 2: Ripto`s Rage (Back from when Spyro games were actually awesome). My fondest memory took place on a warm sunday morning, I was playing Spyro 2 until my brother came in the room and said "The game`s gonna freeze at Breeze Harbor", so I didn't believe him. But right before breakfast, I was in Breeze Harbor and the game froze, so my brother came in to get me for breakfast and said "Told you.".
Games for the SEGA Megadrive used to cost around $100-$120 over here, so I was lucky to get one a year between me and my two brothers (meanwhile, my kid sister is on her third iPhone), and the rest of the time we'd make do by renting. Birthdays were a big deal back then, because if one of my brothers agreed, my parents would sometimes allow us to combine our birthday presents and let us choose one game we both wanted to share.
Anyway, the point is we didn't get many games.
Well, one day, completely out f the blue, my brothers and I are sitting down eating lunch at McDonalds being out shopping with my mum, and she pulls a game out of her bag. For no reason what so ever she'd decided to buy us the Pirates of the Dark Waters game we were looking at in the shops.
All of a sudden a regular day felt like Christmas or a Birthday. I played the crap out of that game with my brothers.
One of the only other moments to come close to being that awesome was when my Grandparents, who normally bought my brothers and I things like history books and clothes, got us Perfect Dark and the RAM expansion pack for Christmas one year.
For want of the price of tea and a slice, the old man died.
Modem Wars 1988 published by EA on Commodore 64. Multiplayer strategy game over 300 baud modem.
We thought that was the coolest thing since sliced bread. Modem Wars and local BBS used to tie up the phone lines for hours and when someone picked up the phone, connection would drop. When the game was over we'd call each other and talk about how the match went.
Toys R Us had an entire aisle of C64 games. You would rip off a ticket under the game you wanted and take it the register where they would go in the back and bring your game. EA games came in a flat folder like a vinyl album.
Mail Order Monsters was a good one, too. Bought it with Christmas money.
For me it would have to be Lunar 2 Eternal Blue on the Sega CD. I remember starting to play it on a Saturday morning around 8 AM and after a very long play session and many complaints from my parents which I ignored I looked at the clock to realize that it was 5 AM Sunday. I was so captivated by the game I actually missed the entire day. The only other game that would keep me focused like that was Morrowind.