Watched only the first half. In my oppinion, the penalty could have changed the match dynamic completely, but United din't know how to change the trend anyway and they did very silly mistakes at the back.
You can't win important matches playing like this. Personally I like a lot more the way City plays than Chelsea. City offers nice combination football and (not always succeeds) tries to attack and be offensive. Chelsea, as all Mourinho teams, tries to take profit of the opponent's errors and that's it. It's a legit way to play, of course, but not one I admire.
Unfortunately, I don't see United near the top 3 this season, even if they sign someone. As other say, United needs at least 2 good signings in the midfield, one at the back and needs to improve the performance of some players like Young and Valencia. Probably the biggest problem is sitting in the bench, thoug I could be mistaken and time could come back to prove me wrong.