I love No 5 and was advised to try First, on the basis that it is a floral, aldehydic, traditional French style perfume. Although the notes are not at all similar, I found I liked it very much.
I tried a sample of No 22, and frankly, didn't like it at all. The appeal of Chanel No 5 is more than just the appeal of a big dose of aldehydes. Once those have faded, the individual notes take over, and especially in the vintage formulations, such as the cologne, the wonderful quality of the ingredients, is what strikes me again and again.
Coty L'Aimant, vintage, is very, very close to No 5, but lacks the real punch and class of No 5. It just falls short of being a twin, a bit like the actress you see playing a famous actress or just a famous person, the mannerisms and general demeanour are the same, but there's something missing that makes the person being portrayed, unique.
I doubt that anyone would produce this style of perfumery today. It is so rich, so strongly floral, albeit not like a flower, but like a concentration of floral tones, so much of another era, that it would probably not appeal to the mass market these days.
Among the vintages I have tried, nothing I have come across is similar, so I'll be interested to see what sort of things people mention. I really don't see any relationship between Arpege and No 5, apart from their floral, 'Frenchness'. There's a chic to No 5 that somehow Arpege doesn't have, in my opinion.