4. High Barrier to Entry
Between the lack of multiplayer support and matchmaking, the depth of the game content, and the difficulty of distribution and installation - it was very difficult for a new player to get into the game for the first time.
If the user doesn't have Warcraft III installed, they had to first install and patch Warcraft III and The Frozen Throne expansion set to the latest version, then download the map file and place it into the correct folder, and finally get online and try to locate a game.
Due to this unique combination of factors, most players couldn't even access the game unless they knew someone who could "show them the ropes". The widespread success of DotA is entirely due to word of mouth and the social nature of the game.
Once a new player actually installed Warcraft III, downloaded the map file, moved it to the appropriate folder, and successfully joined a game, a whole new set of challenges was presented.
Because there was no game tutorial available to give beginner users some introductory guidance, players simply had to join a game (potentially with people who had been playing for years) and play.
With more than 60 heroes available, it was difficult to know how to use your abilities and which abilities your opponents could use against you. Given the complex item and recipe system, new players didn't know which items to buy and in what order.
Lastly, because new players typically didn't play very well and DotA is a highly competitive team game, more experienced allied players could be very critical of them. This often resulted in new or inexperienced players being goaded into quitting the game entirely -- never to return.
5. Game Length
The average length of a game of DotA was about 60 minutes, but games could last as long as 2 hours or more. This unpredictability made it extremely difficult for players to budget enough time to play an entire session, and just one player leaving or dropping from the game resulted in an unfair advantage for the team with the greater number of players.
The unpredictable length of the game also hindered DotA from advancing as a competitive eSport.
Tournaments are difficult to schedule if a round could last anywhere from 30 minutes to two hours, and since the game isn't quite as action-packed as a first-person shooter, many people found it confusing to follow or boring to watch.
When all is said and done -- the good, the bad, the ups and downs, the countless hours spent working on a project driven purely by the desire to create a positive experience for some relatively unknown quantity of people spread throughout the world -- one thing is clear: DotA is fun. The years spent by Guinsoo, Eul, IceFrog, and countless anonymous individuals on DotA, have evolved a small map mod into a worldwide phenomenon.
Estimates of currently active players reach as high as 10 million worldwide (the true number is nearly impossible to determine), and in many regions DotA is more popular than CounterStrike, World of Warcraft, and even the game it rose from, Warcraft III. Despite the accolades and phenomenal success of DotA, it's clear that something is still missing.
DotA has an artificial limitation on its potential. There's a limit to what can be accomplished while nested safely under the wing of Warcraft III.
Players of DotA worldwide have been calling for attention from game developers, hoping someone will take the fundamentally unique, deep, and fun gameplay of DotA, and turn it into something more.
In September of 2006, Riot Games was founded with the hopes of making a game based on the core fundamentals of DotA (great core game design, a strong emphasis on regularly updating content, focus on community engagement) with direct answers to the obvious limitations of the platform on which it was built.
League of Legends, Riot's first title, was announced on October 7th 2008. Players can look forward to a game that was influenced largely by following the positives and negatives outlined in this article.
For more on Riot Games, read Gamasutra's previous coverage:
World Editor - This tool packaged with Warcraft III: The Frozen Throne was the primary tool used for map development. The World editor consisted of four different components, (Information from Wikipedia):
wc3sear.ch - This website, a modding community for Warcraft III, which is now known as Hive Workshop, was the biggest source for character ability icons.