As for gameplay, there will be still only one map to play on, though there will be different match types available, some added after launch. "Denying" is in -- DoTA remake League of Legends decided not to include the controversial mechanic in its gameplay, but Valve's version will let you kill your own creeps to prevent the enemy from getting XP. And AI bots will be available, but not for a full singleplayer experience, just to fill in when human players drop out or aren't around.
Graphics will of course be updated -- GI says Valve has "a sizable art team" working on the game, and there are other design tweaks as well, like the environments getting the saturation tuned down so players can focus on the gameplay. Characters will have all new voicework, too, and not just toss out one-liners in certain situations, but sometimes even interact when they have a past with one of their teammates or opponents (we already know who one of those voices will be). And Valve promises the game will get the same community support as its other titles like Team Fortress 2, including possibly more hat-related shenanigans.
It all sounds quite fun. Too bad we have to wait until 2011 to actually sit in