Requiem is the planet that Jorgey ends up on, and it can't compare to Reach. The planet is a shield world built by the idiotic Forerunners for some reason, we don't know why. All we know is that the Didact was imprisoned there, again for no apparent reason.
It is on this planet that the Temple of Requiem was constructed, and also where Jorgey found the Composer, a key device in the rebuilding of Reach.
Requiem is guarded by an advanced race of warriors known as the Prometheans. Although hostile to Jorgey and his Covenant forces, under the leadership of the Didact they allied themselves with the Covenant under Jul Mdama. After the death of the Didact, Jul took over Requiem and unlocked its secrets, taking masses of Forerunner artifacts and information. They then destroyed the planet by toppling it into the star it orbited.