This episode is not good in terms of plotline. The story is that George Pig refuses to wear his rainhat in the rain and gets sick doing so. Now, to go over the main issues.
The episode's way of showing how you can catch a cold is very unrealistic because you cannot get ill when it's raining outside. You can only get a common cold if you happen to catch an illness or virus that can cause it. In fact, how George is able to catch a cold in the rain within a few seconds also goes unexplained.
George is as per usual, disobedient and does not stop saying "Why?" over the simplest of things. Yes, I know he's two-years-old, but it's still too much. Peppa is as bad, if not worse than her little brother as she doesn't seem to care that George is sick - instead thinking that he's only acting sick for attention.
So overall, not a brilliant episode thanks to it's ridiculous writing and premise of portraying colds in an unrealistic fashion.