The best memories ever are from the Apple IIGS days. Sid's Pirates, SSG's Reach for the Stars, and Electronic Arts' Bard's Tale. These games were so original, and so engrossing, and all done with extremely efficient programming to fit into a 512K disc.
By the late 1980's and early 1990's, Civ I & II were out, soon followed by Master of Orion and Masters of Magic. Several hundred hours could be spent on each game of the series.
Around that time, the Wing Commander series made me buy a 386, a 486 and then a Pentium, just to be able to play all the games in that series. If a game can make you buy a new computer, then it has to be good.
The early 1990's produced Ultima Underworld I & II, which look terribly dated now, but they were engrossing then, and made me jump out of my seat, in fright, more than once.
The original Fallout was right up there with my favorite games of all times. I don't have such fond memories of any of the sequels.
System Shock may well be he greatest shoot/sneak/think game ever. It deserves far more credit than it has received, and its sequel is just as good.
Might & Magic is a wonderful series. As my daughter grew, we often played this together. Heroes of Might and Magic was even better, especially Heroes III and IV. A great game to solo, and a great game to hot-seat or play on-line. Lots of fond memories in our family.
The Europa Universalis series has been great. The designers have been very responsive to gamers, and have tweaked the game nicely over the years. I have wasted (?) well over 800 hours here.
Bioshock is short, but oh so sweet. A superb game...graphics, audio, script, mood, and game play are absolutely top shelf.
Gal Civ I is one of my top five favorites of all time. It is sooo deep, and allows me to play, and win, without having to be terribly aggressive. I much prefer to win games by diplomacy or by sneakiness than to win by smashing everyone else to bits. Gal Civ II is almost as good, but I can't find a way to win without having to do some bashing along the way. The scoring in Gal Civ II isn't as fair to honest players, due the the fact that so much "cheesiness" can come into play. I have close to 800 hours tied up in the two versions.
And what game has been on my hard drive for the longest time? Diamond Mind Baseball, versions 1-10. I have played 4000 or more baseball games, going as far back as the 1930's. The original designer, Ton Tippett (sp?) sold the game, and went to work for the Red Sox, as did Bill James. The game has not been the same ever since. No graphics, but a superior game machine, stats, and the very best play-by-play results. I know APBA and S-O-M fans might disagree, but DMB is still the best baseball simulator out there...but it could be better.
Elemental? Well, I have 350 hours tied up in the game, and probably as many crashes. It really isn't in the class of Gal Civ I or II , as much as I try to like it.