Recumbent bikes are totally different from regular bikes. They don't come in a standard diamond shape with minor variations; there are many shapes and sizes. Here are the advantages of recumbent bikes:

• Very comfortable and supportive of the rider's back.
• Less stressful on the rider’s body, especially on the muscles of the neck, back, wrists, hands, arms and, of course, bottom.
• Enable cycling greater distances, over longer periods and getting much less fatigued.
• Head is held in a more natural, erect position.
• Easier to re-maneuver and faster at slowing down or stopping.
• Excellent for recreational highway and long distance tour riding.

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Source: http://www.bicycle-and-bikes.com/recumbent-bicycles.html

The advantages lie primarily in comfort. Recumbent bikes support the butt and back, removing strain from the back, shoulders, and wrists. Yes, there is an aerodynamic advantage for racers, but few casual riders will notice. Another advantage of recumbents is that the head is in an upright position to keep an eye on the horizon line and the scenery all around. On typical upright road bikes, one mostly looks at a downward angle towards the road surface.

There are several styles of recumbent to suit a variety of riding styles. High wheelbase bikes are primarily for racing and are too tall for casual comfort. Look instead at bikes with a 26" rear wheel and 20" front. They are easier to mount and dismount. You can also look at what are called long wheelbase bikes that have the pedals lower than the seat. Those are usually easier to get used to riding if you're a new recumbent rider. Of course, the easiest recumbent of all is the recumbent tricycle as the trike does all the balancing for you, leaving you to simply enjoy the ride.