The Spain international goalkeeper secured a reunion with former Anfield boss Rafa Benitez in the summer after Liverpool signed Simon Mignolet from Sunderland.
Reina is still under contract at Liverpool until 2016, but reports have claimed that he will replace Victor Valdes at Barcelona at the end of the season in a cut-price deal.
The 31-year-old is enjoying his time in Italy and acknowledged that his wife played a role in his decision to join Napoli.
"I did not expect to change and to come to Napoli," Reina told Cadena Cope. "It was a surprise for me when Liverpool signed a new goalkeeper in the summer.
"My wife was the first to encourage me to move and now I'm very proud and grateful for that decision. I think it has been an absolute success and that I'm a stronger goalkeeper than last year.
"I have been at Liverpool for a long time. But now I am happy here in Naples. I have a fresh outlook on the game and have been playing some of my best stuff. We are having a great championship.
"Am I surprised? Yes. The city is different from Liverpool, people do not respect your privacy, but they show their affection.
"We have a new coach, a new style and new players. I am happy at the moment, but I would be even happier if we won the league, Coppa Italia and Champions League.
"It's very difficult that I'll return to Liverpool. In the summer I will have to finish my contract with them."