It makes me laugh when a top striker misses a good chance and the commentator says something like "you don't expect X to miss from there", when in fact you should expect X to miss, whoever he is. Yes, Aguero's missed a few good chances in the last few games, but that's normal for a top striker. What was abnormal was the period he had before that where almost every chance he had seemed to go in.
I think highlights shows and YouTube are to blame for our skewed perspective (as well as the occasional purple patch that top strikers go through) because they mostly show the successes rather than the failures, making us believe that the success rate is much higher than it actually is. Even the deadliest strikers in the world miss a lot more shots than they score.
Consider the following numbers from league and CL this season(rounded to the nearest 0.5);
Negredo 3.5 shots/goal
Cavani 4.0 shots/goal
Aguero, Suarez, Bale 4.5 shots/goal
Messi, Ibrahimavich 5.0 shots/goal
Ronaldo 5.5 shots/goal
Tevez 11.5 shots/goal
I think you have to make allowances for players who take more long shots, like Tevez and possibly Ronaldo, but it shows that even the best miss a lot more than they score. So I expect Aguero to continue to miss more decent chances then he scores, but he's still one of the best, because that's what the best do.