Fiorentina just barely stayed up last year, but they underperformed relative to the players they have. The biggest reason to watch them is Federico Chiesa. He's going to be an absolute star.
Make sure to watch Atalanta if you can. They played the most entertaining football in the league last season and they're in Champions League now, so there should be extra opportunities outside Serie A. Gasperini is a very likable manager. Zapata was arguably the best forward in Italy last season and I think Luis Muriel will prove to be an excellent buy.
Napoli are always worth a watch, and I'd keep track of Inter too. They've underperformed for years, but they have Conte now and they've made some good buys recently. Barella is probably the best young midfielder in Italy and his all-action game will suit Conte's football.
