There's one interesting omission within the Fallout universe so far - while you can role-play various different human characters, within reason, you've never been able to play as another race, such as a super-mutant or ghoul. Apparently it was planned for New Vegas at one point, but ultimately the idea was scrapped.
Well one new mod for Fallout 3 addresses this oversight. Created by Genin32, the mod introduces a new quest that sees the lone wanderer turn into a Super Mutant during a visit to Vault 87. Those of you who've played the game before will remember that Vault 87 was the experiment into the FEV virus, which evolved humans into supermutants.
It changes the quests in that vault to give players the option to become a supermutant themselves, rather than freeing Fawkes, the supermutant who you can optionally free to assist you in the quest.
By turning into a supermutant, you'll be able to obtain new perks, including steady arm, psychotic, juggernaut and Centaur Affinity.
The downside is that, while supermutants will no longer be hostile towards you, most human NPCs will.
It's a nice mod, and you can check it out here.