What is a classic among computer games?

I have often come across articles and videos reviewing different games from the past as classics, but I am yet to read a definition of what actually constitutes a computer game classic. In one review, the first "Need for speed II", a racing game, from 1997, was given as an example. The impression I got from the article was that the reviewer saw this game as a classic due to having been a milestone for racing games. There was no word about him still playing this game, nor did he describe a community of games still playing it. It may have been a good game for its time, it may have set a standard for future racing games, but so what? We call the symphonies by Beethoven and Vivaldi classics because we still wish to listen to them. Had they only been a stepping stone for greater music composed later, they wouldn't be referred to as classics anymore than compositions from the middle ages or ancient times. The paintings by Bosch are still classics, because people are still inspired by them. "Mona Lisa", by Da Vinci, is a classic for as long as people still discuss her enigmatic smile.

A classic is what's still actively appreciated. The reason why that definition is not applied for identifying what's a classic among computer games, is that almost every game appreciated in the infancy of computer gaming was surpassed by later games developed for far greater computer resources. Very few games from the 1980's are anything beyond, at most, a fond memory of the past. "Elite" was a groundbreaking game from 1984, and greatly inspired the excellent game "X-beyond the frontier" from 1999, which, in turn, is one of many games to inspire "No man's sky". Even the most hardcore fans of the original game would probably prefer to play a newer version of the same game concept, rather than starting another playthrough of the original game.

So are there any true classics from the 1980? Yes. "Tetris", another game from 1984, far less ambitious than "Elite", is still played today. It inspired future puzzle games, many using the same basic concept, but it's not clear to me that they actually surpass the original game. Tetris was a game simplistic enough to come to its right with the scarce computer resources of its time, while "Elite" was a tantalising titbit of what's to come. Elite was an ingenuous milestone, inspiring game developers decades later to make the games that couldn't have been made in 1984.

In the 1990's we saw the birth of many new game concepts. Many of real time strategy games of today are further developments of the game mechanics of "Dune", from 1992. It later lead to command&conquer and "Red alert", as well as inspiring "Warcraft" and many other rts games. A new milestone was set, in my opinion, by the first "Company of heroes", which surpassed the earlier games in complexity, realism, and quality. (It was partly ruined by later patches, beyond patch 1,4. Luckily this was in a time when you could choose yourself what patches to install.)

How many people are playing "Dune" today? Probably very few. However, "Transport tycoon" is played every day online through its open source version OpenTTD, which can be played with authentic graphics extracted from the original CD. It offers larger maps and larger stations, but is otherwise identical to the original game. Like "Tetris" it became a classic because it was everything it needed to be from the very start. In the 80's it could only have been a precursor for what's to come, but in 1994, when it came out, computers had about 4 mb of memory, with graphics card capable of handling 640x480 resolution with 256 colour nuances at an acceptable framerate. This was enough to make a game as complex as Transport tycoon, and also to make it look good. I'm not sure whether there is any transport game that has unequivocally surpassed it. 

The question I'm currently pondering on is: Which games will be considered as classics 100 years from now?