DotA-Allstars' roster of 100+ heroes is being brought over in its entirety. The single map games take place on is functionally identical to the one that you can download for free today in the Warcraft III mod. Items, skills, and upgrade paths are unchanged. Some hero skills work slightly better due to being freed from the now-ancient Warcraft III engine, but Dota 2 will be instantly familiar to any DotA player.

A few things will make significant differences to players making the transition. Dota 2 uses Valve's Source engine, so the game is much prettier. Source itself is getting a few upgrades, including improved global lighting and true cloth simulation. Dota 2's integrated voice chat is a huge step up from having to set up your own Ventrilo server, and the speed of voice communication is very nearly a requirement for a game as team-focused as DotA.

AI bots will take over for disconnected players, and will be available to play against in unranked training matches as well. However, don't get your hopes up for a full-fledged single-player game, though. Johnson says, "Our goal with the AI is just that their experience isn't destroyed just because one person couldn't finish the game."

The bulk of innovation in Dota 2, however, is ancillary to the gameplay itself. Valve is upgrading Steamworks (the company's backend technologies for matchmaking and other gameplay and community-related things) to allow them to create in-game rewards for participating in the Dota 2 community. The idea is to have everything a player does in or out of game tie back into their online identity. Like the improvements to Source, the Steamworks upgrades will be available to third-party developers who choose to use Valve's tools when Dota 2 launches in 2011.

Valve believes that the solution to the huge barrier to entry is threefold. The first, obvious solution is to have excellent skill-based matchmaking for both individuals and teams. Valve believes that the work going into Steamworks for Dota 2's release meets that requirement. Second, interactive guides will allow players to do more than just read a guide for their favorite hero that has been deemed helpful by the community at large. Valve plans to allow guide-makers to tie their work back into the game by doing things like highlighting suggested item purchases or displaying useful information during a match.

Finally, a coaching system is being deeply integrated into the game. By logging in as a coach, veteran players can do their part to help out newer folks. Valve hasn't entirely decided on the specifics of how newbies and coaches will be matched up, but once they're together a few things happen. The coach sees the pupil's screen, and gets private voice and chat channels to communicate with them. The coach probably won't be able to take control of anything directly (once again, the details are currently under discussion), but information is power in Dota 2 and having a mentor whispering in your ear can make all the difference in the world.