I'm looking for the word that would describe something that's impressive but in a negative way. At first I was thinking "ridiculous" but it doesn't necessarily invite ridicule.
This is a really challenging analogy. Infamous isn't the opposite of famous, but rather it means "famous for bad deeds or wickedness". So we're looking for a word that means "impressive, but for something bad".
The closest I can get is "monstrous", particularly with the nuance of a "monstrosity". For example, an enormous building that has impressively awful architecture, like what many think about the "Walkie Talkie Tower" in London
Other possibilities: grotesque, egregious, freakish, outrageous.
is something which stands out from the rest
These do not stand out
The snowfall last night was impressive.
It's normal for this time of year.
The driving skills of cabbies in Mumbai is impressive.
It's quite ordinary, they do it all the time.
The rush hour traffic in LA is quite impressive.
Not really, it happens everyday.
To get a negative, usually more than one word is necessary
and the context of what is meant by "bad" needs to be clarified.