Usually, the number one advantage to traveling in First Class is the quality of the seat relative to Economy Class. The seats are always much larger than all of the other classes and have substantially more legroom, also known as seat pitch. Many of the newer seats have options usually found in high end cars such as electronic reclining, adjustable headrests and electronic adjustable lumbar support. Also, many seats swivel and others have individual laptop powerport connections.
Amenities in First Class can vary quite a bit by airline, plane type, and itinerary. You should not assume that all amenities will be the same for every flight. Make sure to check with all of the airlines on your itinerary before you book the flights if you have any expectations or requirements.
Many of the airlines have upgraded their First Class cabins with very high-end electronic systems which can offer movies, games, TV shows and music on demand, thus allowing their passengers many options for in-flight entertainment. Other amenities you may find in the First Class cabin include personal reading lights, individual satellite phones, noise canceling headphones and of course premium pillows and blankets.
First Class fliers usually have a separate check-in area at the airport or sometimes they may have a separate line for boarding. Some airports in conjunction with the airlines may provide a lounge that offers amenities such as food and drink and as well as web/email access.
Food and drink in First Class is much better than what is usually found in Economy Class. Most of the time you'll be given a menu and will be served on real plates, not trays. And of course the drinks are free which they should be considering what the flight cost.
The final perk about first class travel is when exiting the plane you'll be the first out and consequently the first into the customs lines... that alone is worth the price to some people.