Radha, Heart of Keld's most important ability is playing lands from the top of your library. This card is basically a Courser of Kruphix effect, which is utilized to great effect in commander decks that run Omnath, Locus of Rage.
Radha can also turn into a terribly-powerful creature by using their last ability. It's repeatable, and it allows them to buff themselves as long as you can pay for it. For example, if you have 12 lands, you can pump twice, which will turn Radha into a 27/27 creature.