Basically I watched the entire game. Borussia Dortmund played really well. They always prevented Manchester City from getting the ball. Their defense has shown great potential. I expected them to win the game. But Haland's goal in the last phase of the game put Dortmund behind and ultimately defeated.
Because it was too defensive, so it made Manchester City play quite loose in the middle of the field, and I think if they played loose, maybe they could get a draw, but the second goal scored by Haaland further reduced the chances for Dortmund. There were several opportunities that Dortmund couldn't maximize on scoring goals, this should be of particular concern in the next match against Sevilla.
To lose to Manchester city is not that big of a deal. Manchester city is a superb team made up of top notch players that play as a team to get the desired goal. Dortmund played well and tried their best. They were rewarded with a goal but couldn’t hold or keep up the pressure as Manchester city came from behind and scored 2 goals to win the match. Haaland with the late goal came through for Manchester city to score and win the game against his former teammates. Haaland is undeniably a prolific striker and he’s bound to make a difference in his time at Manchester city.
Why not be a big deal, it's a qualifier which is certainly important to secure full points, and if Dortmund's game was a bit more open and didn't defend completely, maybe they could have got a draw in that game, so against Sevilla on 12 October it would be easier, because if Dortmund lose their next match, it will place them in third place in Group G.