Paris is beautiful.
Any weather, any season - there's no question about it.
Especially perhaps in May, on the edge of spring and summer when everything blossoms so wonderfully and days are longer and warmer but freshness is still in the air.
I always thought Paris has been a bit overrated as a city until I visited myself. Well, my verdict is Paris really has A LOT to offer: best cuisine, fine architecture, famous fashion, great weather and european chic. One of the best wines I tried in my life is from Paris too :) as well as always tasty food, be it a small cafe at the corner of the street or elegant, gourmet, avenue des Champs-Elysees restaurant.
Paris is charming, unique place but I am afraid you won't find here London' or Berlin's efficiency. Following the tube guidelines might be tricky and if you ordered the tickets to Louvre online and wanted to pick them up in Paris, you might be surprised to find the actual kiosk is closed, with no sign of the cashier around. While you rock your brain how to sort the problem and if you want to spend hours queueing, them enjoy their first glass of wine in sun-lit bistro terrace somewhere (and unlikely get back soon!)
The point? You just got to enjoy it the way it is. This is the thing about Paris, it's not formal a tiny bit - it's all about going with the flow and enjoy every moment. After all...
La vie est faite de petits bonheurs! : )