The Colombia international signed from Sevilla in July 2015 for a reported fee of €30 million (A$45.12 million) and scored 34 goals in all competitions, helping them to a Supercoppa Italiana triumph last year and a place in this season's UEFA Europa League.
The 31-year-old returned to LaLiga with Villarreal in the transfer window as Milan conducted an overhaul of the squad after the takeover by Rossoneri Sport Investment Lux.
Bacca has pulled no punches in his assessment of the quality of Milan's squad during his two-year spell at San Siro but says helping them return to European competition shows his time in Serie A was successful.
"The past few years at Milan were satisfactory for me personally. I achieved my objective," he told W Radio in Colombia.
"Things could have gone better but you need help from the directors.
"I was at the worst Milan in history. After 30 years, president Silvio Berlusconi wanted to sell the club. We had different ideas with the coach and the new owners, but I left with my head held high because Milan are in Europe and I gave my contribution.
"I'm pleased Milan returned to Europe. That was my goal when I left Sevilla."