Radiant

The Radiant team is located on the bottom-left side of the map, which has a brighter, happier theme. The Radiant side of the map contains fully grown trees, green grass, and bright blue light glowing near the Radiant ancient. While the lighter theme may carry good connotations, the Radiant heroes are not purely good.

From a gameplay perspective, there are many key differences between the Radiant side of the map and the Dire 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.
 * Unlike the Dire side, Radiant's top lane has a convenient way to pull using the nearby Hard Camp.
 * It is possible to block 2 jungle camps with 1 ward on in the Radiant jungle.

Currently, 57 of the 107 heroes in Dota 2 are Radiant, with an additional 2 Radiant heroes in W3 DotA. A list of Radiant 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.