«Juanjo Sáez has always drawn on his own past and memories when spinning tales that connect with the reading public for precisely that reason, thanks to his sincerity and the universal nature of his stories.» Sergio del Amo, El País

«A tragicomic portrait of the threshold that stands before us as childhood comes to an end. […] Tender-hearted Metalheads, the new animated series from Barcelona cartoonist Juanjo Sáez, is an affectionate account of the adolescence of two die-hard Iron Maiden fans in pre-Olympic Barcelona. A highly personal work of animation with a minimalist, witty aesthetic.» Guillermo Altarriba, El Mundo

«Clean, seemingly unfinished sketch-like drawings that feel no need to fill the screen, as if to do away with anything but the bare minimum. Each new shot is a surprise. […] This is a minimalist piece; a rest for grateful eyes tired of the constant visual opulence television seems to crave (…) Offering generous helpings of narrative ellipsis, the viewer’s initial reaction is a purely aesthetic one: why was it drawn like this and not any other way. And the freedom offered by the drawings is absolute. […] A touching work of craftsmanship that is not to be missed. A marvellous miniature.» Tomàs Delclós,  El País