Hé, that's a nice idea of a thread, I find.
You'll get lost cause it sprawls a lot, even when it's dense.
You'll often feel young cause much of it is old.
Your eyes will be pleased by the many nice looking girls.
You'll be pleased by much of urban beauty.
You'll still laugh at some French pompous manners and excessive pride.
BTW, at the beginning, you'll probably strangely and awkwardly look around, like - fuck, all those around me are French...
Then you'll learn French if you haven't yet since many locals wince at English.
You'll sometimes feel kind of breathless, oppressed cause it can be tense and might require to be foxy, if not nasty sometimes.
You'll convert to mass transit cause traffic is hellish.
Depending on your morphology, your job and/or your hobbies, you might have to watch your daily meals cause French food is surely nice but often too fat.
You'll find some kind of help if you're poor.
But you won't find a job if you're unemployed, so...
You'll be outrageously overtaxed if you're not poor.
You'll be highly annoyed by the French monstrous and overly costly public bureaucracy.
You'll learn what actual equality means, but unfortunately some hypocritical a--holes will make you undergo unfairness on behalf of that ideal of equality.
So you'll probably not be able to stay if you're an entrepreneur who's not established yet.
You'll both love and hate it.
You'll take the Eurostar to London when you hate it too much.
...
Well, those are some of today's obvious coming to my mind, but there's definitely much more.