Abilities

After Sasuke and Gaara, Dosu was the third most powerful Genin in the exam arc. His main attacks came from his ability to manipulate sound, with help from the metal gauntlet, the "Melody Arm" on his right forearm, which he used to generate sound for these attacks. His abilities attacked the inner ear, directing his sound deep into it, he could cause great pain, disorientation, and nausea. During their match, Choji attempted to block his attacks by pulling his head inside his meat tank jutsu, only to be thwarted by the fact that by directing sound through the water in his body (Choji, having accidentally crashed into a wall at this point, allowing Dosu to hit him at extreme close range) Dosu could still generate the effect. Choji was instantly KO'd by the attack.

Personality

Dosu seemed very loyal to Orochimaru's cause, and to a lesser degree, his teamates. Though he says himself sound ninja are willing to sacrifice their own team mates to the cause, he promises to avenge Zaku after his debilitating defeat at Shino Aburame's hands, and seems to have had confidence in Kin before her match with Shikamaru. He showed dedication to Orochimaru's task at first (sacrificing Kin would have disqualified the team from the official exams, pointing towards his main task being the assassination of Sasuke) but perhaps became disallusioned with his sensei after he sees that he has given Sasuke a curse Seal.
It is unknown whether he planned to stop following Orochimaru, or whether he simply wanted to prove himself better than Sasuke for Orochimaru's purposes, but following the preliminaries he attempts to kill Gaara to get to fight Sasuke earlier in the finals. Dosu, however, seeing only Gaara's fight with Rock Lee was oblivious to the former's Shukaku, which easily killed him in one blow.