For this to make any sense at all, you'd have to decide what you're measuring, in terms of "impressiveness". Are you measuring the aesthetic qualities of metro systems? If so, the Moscow, Montreal, Bilbao, Washington would all gain at the expense of places like Tokyo, Toronto, and Paris. If you are measuring how well they perform the job of getting people around, then surely Tokyo would be somewhere near the top, while some of the prettier metros would decline. Even if you do aesthetics, you'd have to state your bias, whether you liked old, and perhaps even grimy stations that hint at subway life some time ago, which would surely vault New York up the list (and Buenos Aires, too, where if you're lucky you'll get into an all-wooden car from the 1930's, still in service) - or whether you were after new and sleek, in which case Bilbao etc. would bump up the list.
I find often that people simply don't say what they are measuring, so you have these arguments that make no sense, like "You can't even compare Bilbao to Tokyo because they don't carry enough people!".
In the context of North America, Toronto impressive in how many people it shifts around daily, but aesthetically it is nothing special. Either way, it would not make the tops of any worldwide lists. That's OK, gets me where I'm going.