from my experience i think whats fun bout dota isn't the game itself..its more about the diversity of players / hero 
now u walk into a cyber cafe, there won't be many games u can find that lets u on a 5 on 5 basis game on an average of 1 hour game.  Plus you can find strangers, noobs, pros all mixed up within a game that makes the game confusing or exciting depends on how u view it    Also all battles are diverse enough, a good drink session can be all about dota after the game. We could talk about the mistakes done, the proper purchase, the effective strategy ,the noob players etcs , well could take whole day talking bout it. So regardless of the result of a game, i will have satisfaction after each game.

now based on large scale games i played with previously, example half life , team fotress or battlefield. Due to the gameplay style of these games (perhaps im comparing the wrong genre    ) , you could see the same player doing the same shit for the whole game on and on to own non stop.  The 'sien' factor is very high . One reason dota survived till now is due to its -ar mode . And due to the popularity of dota, u almost cant find any game other game played in cafe nows..lol . I recall in the past few years where we actually go from cafe to cafe finding c&c generals opponent, such a pain in the ass. Since dota is still continually updated till now, it is good investment playing in it, a game which i predict can last a while more, where you can ensure with each game u play, u will improve for the next game.