Champagne and caviar aside, what makes flying first-class so much fun?

First-class travel on Cathay Pacific, Singapore and Emirates is vastly different to flying first-class on US airlines
Sure there is a flatbed, bubbly, caviar and top-notch service to spoil you. But what is beyond this, that makes flying first class so much fun? A frequent traveller answers anonymously on Quora.
I used to be a heavy business traveller in Asia and frequently got first-class upgrades on some of the top airlines in the world due to high frequent flier status. Low premium cabin demand in late 2008 because of the financial crisis made for amazing upgrade opportunities. First-class travel on international flights, especially on Cathay Pacific, Singapore, Emirates, or British Airways is completely different to anything offered by US airlines where first-class means a slightly larger seat and a modest meal (vs nothing at all).
Private security lines

Some airports have private security lines. At some places, this just means a shorter line. At others, this means a separate, more private screening area.
Lounges

Cathay Pacific has two dedicated first-class lounges, The Wing and The Pier. Anyone who is a Cathay Pacific Diamond / OneWorld Emerald member can use them, in addition to paid first-class travellers (I’ve bought a US$70 economy ticket to Bangkok and enjoyed almost that much value out of the high-end food and drinks).
At The Retreat, inside The Pier, there is an elegant in-house spa, eight private day suites where you can relax and unwind, plus à la carte dining. At The Bar, you can enjoy cocktails unique to The Pier.