I have been a gamer my entire life. Everyone enjoys different aspects to games.
A wise man once described people as being in different states of desire, the base state of desire being instant physical gratification, then a desire for money or power, following that, a desire to help others or their community
People enjoy modern shooter games for graphics, violence, testosterone, and competition. Occasionally physics or science/fantasy stories projects a solid shooter into a legendary status. (The original Halo was a solid game with stellar graphics, good physics, relatively balanced competition and a story that revolved around an idea that was new to most of the market segment. It was a huge hit and its legacy lives on) These style of games primarily market towards instant gratification.
MMORPGs are popular because they hit on the desire for money and power. Invest more time into the game and you can acquire more gold, better gear, higher levels, better skills, titles, own a house, run a guild, control a market segment in the auction house, etc. World of warcraft streamlined the genre by realizing that the people who play these style of games want it to be simple and easy, but allow for multiple avenues of achievement. (Urist McPaladin: "I'm the best paladin tank on server X and I have a full set of tier 10097879 armor of uberpallytanking" Uristet McWarlock: "Well my arena team is ranked #1 on server Y, and I have over 10^9 gold.")
Every game in that has exploded in mainstream popularity is because they hit on the primal urges and desires of a large market of people. Ever hear of a game called cow clicker? instant gratification. Farmville? essentially a build up of resources that allows people to pretend they have a modcium of wealth.
Dwarf fortress is fantastic for a few reason. DF is the ultimate sandbox game, it allows for an amazing level of creativity, almost to the point of being art, the math behind the world generation and all the facets of the fantasy world are astounding, it gives the player a stunning amount of control, satisfying the desire for power, wealth acquisition is there too. Instant gratification is subdued, but its there as well, whenever you strike a vein of a valuable mineral, or press that button that creates !fun! in its many many varieties.
What makes Dwarf fortress stand heads and shoulders above any other game in my opinion is the creator. As a community we have a game that none of us could made on our own, Toady has proven himself to be in the third category of people, whose desire is to give back to the people. Think about how much work has gone into this game, how much math, programming, testing, updating, etc. Consider that creating this game has been a full time job for years, and he has no intention of stopping any time soon. He could have used his skills and intellect to do any number of things, he could have been an extremely wealthy individual working in the financial sector, or a programmer working for electronic arts making the latest pile of shit game to try and sell you for $60, but no, instead he has devoted himself to a creation that he is openly sharing with the world, for anyone who wants it.
I enjoy Dwarf Fortress not only because of my base desire for power, but because it reminds me that there are greater things to aspire to. Thanks Tarn Adams.