I predominantly watch Spanish, so I'll be really interested to see how Mandzukic, Griezmann, Siquiera and Oblak replace Costa, Villa, Filipe Luis and Courtois and whether Atletico can sustain their challenge for a prolonged period. There's talk that Simeone wants to play more in wider areas and change the focus slightly, and Griezmann and Siquiera could be a particularly interesting combo.
Obviously the El Classico freakshow is going to be interesting as well. Rakitic at Barca, Kroos at Real, Suarez v Rodriguez. All a bit tacky, but will definitely make for some amazing games. Have no idea why Barca have spent so much on Jeremy Mathieu. Never looked anything special to me at Valencia, and he's soon 31. Bizarre.
Looking forward to seeing Jese Rodriguez a lot more, when he gets back from injury as well. Also interested to see how Rodrigo gets on at Valencia.
Going to try to catch some more Bundesliga as well, if I can. I imagine Lewandowski will have a stellar year, very interested to see how Immobile and Ramos do in his stead at Dortmund. I don't know the other Bundesliga sides well enough to comment, but I'm hoping to watch more and learn a bit this season.