They've looked good tonight, but I think a few things need to be remembered before the customary start-of-season "City's going to blow everyone away" reaction.
First, City is much more prepared to play Guardiola ball than we were to play LVG's football or even Mourinho's football. Pellegrini drilled that team to play nice, fluid, possession football, and to press high up the pitch on defense. Pep's working with players who already have an idea of what he wants and have been executing a similar system for the last few years.
Second, this is Pep v. Tuchel. Two managers who know each other well, and thus Pep had intimate knowledge as to how to stop this particular Dortmund team. We still have yet to see how his style and system will play against the pace and physicality, and the end-to-end nature of the PL.
But as I said, they've looked quite good. I don't expect them to blow the league away this year, and I do expect us to match them blow for blow when we meet in the first Manchester derby of the season, though.