Only flew international First Class once - back in 1990 I got bumped from business to first on Pan Am from Seattle to London Heathrow. The meal service was incredible - a full seven course dinner, for the salad course they had a 'salad bar trolley' with the ingredients and made your salad to order. One of the main course options was prime rib - again on a trolley, they brought it to your seat and you pointed at the cut you wanted. Seats back then were nothing special compared to today's lie-flat, but it was still pretty nice.
Best business class I ever had was SQ - 2 class 777 from Singapore to Las Vegas (with a stop in Hong Kong) - so pleasant I was actually a little disappointed when we landed.
All that being said, the whole idea of first class is to get you where you're going in relative luxury. Unless you want to go to the destination in question, why bother? If you want a great meal, go to a five star restaurant - the food and service will be even better than the best airline service at a fraction of the cost. If you want to be pampered, go to fancy hotel with a nice spa - again for a faction of the cost. And at a restaurant or hotel/spa, you can leave anytime you wish - hard to do at 39,000 ft.
If you want to experience good first class air travel, pick a luxury destination you'd really like to visit (Hawaii or similar comes to mind), then see who offers a first class product to that destination.