The debuff is cosmetic only and will fade after a short period of time.
Prior to Patch 4.1.0, this allowed the death knight to raise a fallen raid or party member to fight for a limited time as a ghoul. This creature could perform a number of attacks including fear, apply disease, stun, cause a target bleed, explode, and pummel.
0400Patch 4.1.0 (26-Apr-2011): Now reworked as a battle rez. Players are not raised as ghouls. Changed from Raises the corpse of a raid or party member to fight by your side. The player will have control over the Ghoul for 5 min. It shares the same global battle resurrection cap with Rebirth and Soulstone.
0400Patch 4.0.6 (8-Feb-2011): When a character is raised as a ghoul with Raise Ally, there is no longer a considerable pause after losing control of the ghoul before being returned to the corpse or graveyard.
0300Patch 3.3.0 (08-Dec-2009): The cooldown on this ability has been reduced from 15 minutes to 10 minutes. Cannot be used in Arenas. While this spell is active on a target, they will not be sent to the graveyard, prematurely ending the spell.
0300Patch 3.2.0 (04-Aug-2009): Using the Gnaw ability while under the effects of this spell will now initiate auto-attack. In addition, the damage done has been changed from a flat value to a percentage of weapon damage.
0300Patch 3.1.0 (14-Apr-2009): Now has a cooldown greater than 15 min and can no longer be used in Arenas. The buff from this ability can no longer be right clicked to cancel. In order to end the effect, the player controlling the Risen Ghoul must right click on the unit portrait and dismiss the pet. In addition, using this ability on a player whose level is too low will now give a “Target is too low level” error message instead of “You have no target.”
0300Patch 3.0.8 (2009-01-20): Raise Dead has now been split into two spells: