In the 2002 World Cup, for which he was picked ahead of Riquelme, Aimar appeared against England, subbing in for Juan Sebastián Verón in the 1–0 loss, which led coach Marcelo Bielsa to start him against Sweden at the latter's expense.
An elegant, technically gifted, and creative attacking midfielder, with a small frame, Aimar was a right-footed player, with vast array of skills and an eye for goal. He excelled in a free role as an advanced playmaker, where he was best able to utilise his dribbling skills, vision, and passing ability to create chances for team-mates and orchestrate attacking moves. His skills and playing style saw him earn comparisons with Diego Maradona in his youth. Due to his talent and flamboyance, he was given the nicknames El Payaso (the clown) and El Mago (the wizard) throughout his career. As a youth, compatriot Lionel Messi stated in 2002 that Aimar was one of his biggest influences as a player. In addition to his playing ability, Aimar also drew praise for his leadership qualities; however, despite his talent, he struggled with injuries throughout his career.