Many causes for concern for me. The failure to improve a dodgy defence for one and messi's injury concerns plus Madrid seeming to have frightening options and good signings over the summer.
The defence is improved already, both considering the collective effort (pressing/counter-pressing/forechecking) and the individual effort (anticipation/positioning) + the long overdue shift to man-marking when defending corners. The failed collective defensive approach of the past was recognized as such and solutions are seemingly worked on. It's all still work-in-progress though. Sadly, personnel decisions were not taken so we're stuck with what we have. Lets hope the coaching staff can bring out the best in those players.
Leos' injury problems are a cause for concern, as it's impossible to compensate for him. My biggest issue when seeing him out though is that we still field a system based around a false-9 which can only ever end in a backlash - no player will be able to fill his shoes. But this is merely a bad habit. Therefore, the question is whether the team should even try to compensate for him. In my opinion, a different approach should be taken in these particular circumstances. There's enough quality left in the team to do so and possibilities are abundant system-wise.
Generally speaking, I'm fairly optimistic concerning this season mostly because of Tata who I trust 100 %. La Liga and the CdR are both realistic goals; what happens in the CL remains to be seen as competition will be ultra stiff there.
Nevertheless, what was on the horizon two seasons ago manifests itself more every day. The days of Barca walking over any opponent bar a handful are gone, so I hope everyone cherished these days because I don't see them coming back either. From here on out, every match bar a handful will be competitive and a challenge and our players will have to push it to take the win. Let's see how much fight there's left in this team.