Did you list what you consider to be the best twenty games of all time or did you leave off older classic games with inferior graphics and go with newer titles?
I don't consider my list to be of "best games of all time" or I'd have more LucasArts adventures on my list. Instead it's more a sampling of what I think are the best of various types. I have some humorous games, some puzzle-oriented, some on the easy side, some for those who like tough puzzles, and some because they have some unusual feature of gameplay. e.g. - I wouldn't say Return to Mysterious Island was one of the best games of all time, but it was unusual because you could combine inventory items to create an object to solve a puzzle, disassemble the object, and then recombine the components with different inventory items to produce a new item to solve a different puzzle. It's the first game I know of to do this, and did it better IMO than Destination Treasure Island or Voyage. Most games are far more restrictive in how you can use inventory, or how you can solve a puzzle (Return to Mysterious Island allowed different solutions to problems).
I limited my number of older titles so I could include the newer titles I thought a gaming newbie might enjoy. But I still ended up with 13 older ones and 7 newer ("older" meaning pre-year-2000 for purposes of my list). So you could say newer games got preferential treatment. But I also eliminated TLJ, Riven, and Syberia to make space because other people were sure to vote for them, and two of those were what I'm calling "newer." And I eliminated Atlantis 5 from the "newer" list, though I think it's one of the better newer games. I just couldn't stand to prune my "older" list down any further.
I didn't let ease of getting the game to work come into my choices, though I have on past Twisty lists. It's become too hard to predict whether a game will work on someone's computer without knowing more about their computer, what with video card requirements and restrictions imposed by SP2.
I didn't consider availability at all. Hence the presence of Obsidian. And I thought it was important to include a few old classics. So I have GK1, Secret of Monkey Island, and Myst on my list.
I described some of my other considerations for choosing games along with my list. It's at the bottom of the 3rd page
***here*** if anyone is interested.