AFnord: Most of the requested games are just there because of nostalgia reasons. People list the games that they enjoyed playing back in the days. And many older games have aged horribly, and only a person who was there, who has nostalgic ties to it, can fully enjoy the game. There are of course many games that have stood the test of time, that are fun 20 years after their release (Ultima 7 is a good example), but I would say that most are not, in particular not the very early entries in a genre.
jefequeso: I have to disagree. As someone who played very few games as a child, and only really started getting into gaming maybe 5 or 6 years back, I'm playing many old titles for the very first time. And I've found that the vast majority of "classics" are just as good playing them for the first time today as I assume they were "back in the day." Sure, there are many cases where you need to adjust to mechanics or philosophies that are different from the "silky smooth rollercoaster" approach of modern games. But if you're willing to do that, most older titles that honestly did things well (as opposed to just being the first to do them. It's the difference between, say, Metroid and Super Metroid) turn out to have aged quite gracefully.
The games people remember and talk about are usually the outstanding games, the ones that did that extra bit that made them great, and those are the ones that have stood the test of time well. Magic Carpet, Might & Magic 3-5, Ultima 7, Civilization 2, they are all great games, well worth the time of even a modern gamer, but what about Might & Magic 1? While that game has its charm, sure, but if you don't have any nostalgic ties to 80's CRPGs, it is a hard game to get into. I recently got some first hand experience with one of the most important CRPG series of all time: Wizardry. I found the usually super expensive Wizardry collection for 1€ (I'm a lucky git), and tried the first game. And I just found myself thinking "well, this game is not very good". Things like tooltips for displaying what the heck items actually do, less artificial lengthening of the game in the form of grind and more variety, I was really missing it.
Metroid 1 was a smash hit back in the days when it was released, most NES owners loved it, it was great. I have enough nostalgic ties to that game that I can't hate it (I still remember the day I got it, it was early summer, I was sitting in the kitchen and I was 5 years old. My father told me that he had a surprise for me, and told me to close my eyes. When I opened my eyes again, Metroid was on the kitchen table. I did not go out for a week, I was glued in front of the TV. Sure, the copy was used, it lacked the box & manual, but I did not care, it was the game I wanted), but I "know" that Super Metroid is the better game. The genre had evolved, it had cut away some of the annoying bits, tightened up the gameplay a bit and so on. So why would anyone really go back to Metroid 1, apart from either nostalgia or historical reasons?
And look at King's Quest. While the early entries in the series do have their charm, and they are genuinely funny from time to time, they also suffer from some gameplay mechanics that are very hard to accept, even by early 90's standards. Things like dead ends were perfectly acceptable back then, but unless you have nostalgic ties to the games, you will probably not enjoy them very much, not without a walkthrough.
Civ 1 just suffers from being surpassed. It is not a horrendous game, but as there are so many games that are better than this game, why would you play it?