Over the decades, he directed nearly 300 films and television programmes. His documentaries, often described as mirrors of reality, provided intimate glimpses into the lives of ordinary people, marginalised communities, and those whose stories were frequently overlooked.

"His great documentaries, especially from the 1970s, many of which were shown publicly only after Croatia's independence, perfectly captured the time in which they were created, with all political, social and cultural aspects", said Nina Obuljen Koržinek, Minister of Culture and Media of the Republic of Croatia.

During his lifetime, Krelja received numerous prestigious awards, including the highest national recognition for artist excellence, Vladimir Nazor Award, issued by the Ministry of Culture of Croatia, and the Golden Oktavijan Award for lifetime achievement, issued by the Croatian society of Film Critics.