The 31-year-old striker played for Barca for the 2009-10 season before leaving AC Milan on loan after falling out with then coach Pep Guardiola, eventually joining PSG last summer.
"In personal terms, Ibra is a great guy," Busquets told Le Parisien. "He's a serious guy, who makes fun of you when you least expect it. I really had a great year with him.
"In sporting terms, it's clear he wasn't able to give the best of himself. You could sense he was unhappy. The coach didn't count on him anymore, he wanted to change the system and put [Lionel] Messi through the middle of the attack. But Zlatan wasn't bad when he was with us.
"He could have stayed at Barca. An Ibra-Messi tandem would have been marvellous, but history decided otherwise. In the dressing room, I never saw Zlatan get annoyed with [Carles] Puyol, Xavi or [Andres] Iniesta. Perhaps we had a different dressing room to the ones he'd been used to or the one at PSG."