Guardiola's first season will probably be the most interesting one.
He got Barca playing tiki-taka immediately, but the nucleus of the team were either supremely skilled, or already used to the high possession methods with Spain/their Barca culture. His biggest success was seamlessly integrating Pedro, Busquets, Pique into the team, and the various rejiggings of the forward line, imo.
At Bayern he did well to get the players playing his way. But after Barca, it was probably the second most technically and mentally suited set of players in the world to his philosophy. The likes of Lahm, Thiago and Alaba are supremely intelligent and technically gifted. It would have been a comparatively easy transition to a high possession game with many micro-tactical instructions.
At City, he comes to a team with an abysmal midfield and a leaky defence, and on top of that, a team which is nowhere near as technically talented and patient as the ones he's coached before. And due to the Euros, he'll have a shortened preseason with some pretty worn out players. At Barca and Bayern, Pep has previously tinkered for tinkering's sake (or to achieve supernatural footballing perfection rather than victory, as qua would say). He won't be able to do that in England, his squad isn't physically and technically superior enough to do that here, like it was at his past two jobs. The likes of Zabaleta, Kolarov, Fernandinho, Kompany are not Pep players. They're PL players. Will Pep bend his ways to the league, will his signings adapt, can Pep put victory above his footballsexual desires, what happens when Pep realises that his backline pushing up is a really bad idea, how will Pep do without having a squad that's a level above the rest? They're all genuine risk factors for his first season. They make next year anyone's game.
Pep's the best manager in the world and there's no doubt he will adapt at some stage. But maybe not in his first season, and that's where we all have a chance.