Rouvas had no vocal lessons as a boy and taught himself primarily by ear, so during the recording of his first album he had to learn music theory in a short time. His voice developed significantly since his early teenaged performances. Rouvas' detractors have criticized his voice as average, or limited, contending that his appeal is based on image. Whatever the assessment of his voice, it has often been overshadowed by showmanship and appearance in the media; many preferred to watch him perform than to listen to him. These criticisms diminished by the second decade of Rouvas' career; his technical skills (range, power and versatility in particular) and expression are better appreciated. Rouvas has a tenor vocal range; although he can also sing low, in the F-clef range, he prefers to sing higher and can reach notes beyond the typical tenor high without falsetto, varying his dynamics from whispers to belts. His vocal power was evident in early recordings, notably on "Mia Fora" from Aima, Dakrya & Idrotas (the first album to showcase his vocal ability). During his 1997-98 hiatus, Rouvas received voice lessons from American coach Raz Kennedy focusing on rock and blues techniques. His subsequent sixth album, Kati Apo Mena, was a milestone in Rouvas' vocal development; he exhibited a consistent depth and dimension which previously appeared only sporadically on his first five albums. He won the Pop Corn Music Award for Best Male Vocal Performance twice in a row: for 1999's "Den Ehei Sidera I Kardia Sou" and 2000's "Se Thelo San Trelos" (the latter from 21os Akatallilos). By Live Ballads in 2006, Pavlos Zervas of Music Corner considered that Rouvas' voice had reached its most-mature form. Critic Tasos P. Karantis of Orfeas conceded that Rouvas sang with competence and technical precision, and his voice was easily recognizable. Ilias Malasidis of Athens 24 noted that Rouvas' voice was initially more intriguing than his material. His voice is best-suited to power ballads, his signature style due to his sensual tone. Reviewers have praised Rouvas' live performances, particularly his ability to execute "especially difficult and demanding songs", hold long, high notes and dance while singing. Down Town commended him for never using a playback track, common among Greek artists, but Billboard noted that an ability to sing well in English would increase his international appeal. During his career, Rouvas has perform in a number of genres, contemporary and traditional; in some songs (such as "O Iroas" from Iparhi Agapi Edo), he delivers spoken verses which have been described as a "light rap." He has also performed as a crooner styles and a classical tenor. Rouvas' defining characteristic as a vocalist has been his emotional expression. He maintains his voice with a strict organic food diet and avoiding alcohol and smoking, banning smoking in his dressing room. Singer-songwriter Stelios Rokkos, who collaborated with him for three seasons, described him as "probably the most disciplined singer I have ever met--in fact, to the point of insanity." CANNOTANSWER

Answer this question "What criticisms did he receive?" by extracting the answer from the text above.

Rouvas' detractors have criticized his voice as average, or limited, contending that his appeal is based on image.