was described as "important in the development of the band" presenting "the band's musical growth as they explore the parameters of orchestral, neo-classical metal." With the release of the band's second album, Mother Earth, their musical style came to a point of inflexion, where only den Adel remained as lead vocalist leading the band to more melodic and Celtic songs and more folk influences. Critics approved of the changes in musical direction and suggested that the album "reveals new dimensions in the concept of metal." With Daniel Gibson as its main producer, the album The Silent Force was classified as "very melodic, catchy and relaxing" With the release of The Heart of Everything, in 2007, critics were divided on the band's new direction, though some appreciated the new direction and found it more varied. About.com agreed with both opinions, stating that the album had "the depth and complexity of classical music and the dark edge of gothic metal." allMusic commented that the band "isn't afraid to get downright symphonic". In 2011, the band released their fifth studio album, The Unforgiving, the biggest change in their musical direction to that point. Although being largely well received by critics, some reviewers disliked the changes, with Q magazine calling the album "The metal T'Pau". Besides that, some critics found the "1980s pop, rock and metal" influences a good thing for the band. In order to celebrate the band's 15th anniversary, the Belgian radio station Q-music invited the band to make 15 covers of famous songs. Later, the band released The Q-Music Sessions album, another divergent genre variation from their original sound. The album featured reworked covers of several famous pop songs, such as "Titanium" by David Guetta featuring Sia, "Grenade" by Bruno Mars, "The Power of Love" by Frankie Goes to Hollywood and also some indie and folk rock songs as The Who's "Behind Blue Eyes" and Passenger's "Let Her Go". The name of the band's sixth studio album, Hydra, refers to this great variation in the band's main sound, as Westerholt said: "'Hydra' is a perfect title for our new album because like the monster itself, the record represents the many different sides of our music.” American magazine Aquarian Weekly considered the title highly appropriate and compared it to the band's diverse musical history, alleging that they were able to find the right balance between all the musical changes and, during the