Former player Marcelo Rios doesn't find Federer, particularly entertaining to watch on the court as opposed to players like Nick Kyrgios or Fabio Fognini.
Rios is a very interesting character on top of being a really good tennis player in his time. He spoke recently about the entertainment side of tennis noting that Federer isn't really that much entertaining. At least not for him personally because you won't see too much drama on the court when Federer plays:
“Federer for me is not a player that you see and you say ‘how entertaining’. I like the way he plays because he’s a guy with incredible ease, very intelligent on the court, very good. But he is not a Kyrgios, a Fognini that you see him and you are waiting for him to make a fuss, to leave a mess. That’s more entertaining”.
He doesn't see Djokovic as particularly entertaining either:
“I don’t find Djokovic an entertaining guy on the court either."
He also talked about the restrictive side of tennis:
“Tennis has always had restrictions. If you swear, you get a fine; if you throw your racket, another fine. In press conferences you couldn’t talk bad things about anyone. Wimbledon makes you dress in white making you look like I don’t know what. Tennis is boring, it’s like watching cricket. Then a guy like Kyrgios comes out and revolutionizes everything. He packs stadiums, it’s a spectacle. My personality was also a bit ‘wrong’. I used to attract a lot of attention by throwing racquets, or by saying ‘old fuck’ (to an annoying lady in the crowd). People were entertained”