Dire

The Dire team is located on the top-right side of the map, which has a darker, gloomier theme. The Dire side of the map contains trees without leaves, decayed dirt, and glowing lava near the Dire ancient. While the dark theme may carry evil connotations, the Dire heroes are not purely evil.

From a gameplay perspective, there are many key differences between the Dire side of the map and the Radiant side. The layout of both sides are very different, and can be viewed here. Here are a few key differences.
 * Roshan is located on the Dire side, near the bottom rune spawn location.
 * Dire's bottom lane has no convenient way to pull.
 * It is impossible to block 2 jungle camps with 1 ward on in the Dire jungle.

Currently, 50 of the 107 heroes in Dota 2 are Dire, with an additional 3 Dire heroes in W3 DotA. A list of Dire heroes can be found here.

In W3 DotA, when playing the Normal Mode gamemode, players could only pick Dire heroes while on the Dire team, and vice versa. At the moment, there is no such gamemode in Dota 2.