Reptiles are a very diverse and successful group. They have been around for billions of years and they have survived through many events over the course of their existance. They come in many different shapes and sizes, though they all are similar in that they are ectotherms. They are limited in their environment by temperatures because they do not metabolize their own body heat and therefore must use another heat source, such as the sun. Heat warms their bodies to the surrounding temperature and gets their muscles working. They travel between different thermal gradients in their environment, warming up and cooling down, as they go about their daily reptile business.
Reptiles can make captivating pets. However, reptiles are definately not for everyone. Many species require special environments and diets to prosper. It takes dedication, and understanding, along with a deep passion for animals. Before you buy a reptile, or any animal for that matter, please research its requirements thoroughly. You don't want to get something and realize after the fact that you are not that dedicated to its well being.
Why to reptiles make good pets? If you are looking for an animal that will show affection and likes to cuddle, then you are looking in the wrong place. Sure you can interact with them, but not in the way you interact with a dog. Reptiles do have personalities, though it appears to me to be somewhat limited in snakes (IMHO). I have not seen a reptile display true affection. Sometimes they may do things the make people think that they see us as more than just "things". One can get a lot of satisfaction just from caring for a reptile, interacting with it, and watching it grow. Although some reptiles do require a lot of care, snakes are much less demanding reptiles. With any reptile you need to provide a thermal gradient in the cage. This is usually done with either light bulbs or under the tank heaters. Also it is necessary to provide the appropriate humidity required by that species. The animal must of course have the proper size enclosure throughout all stages of life. Some species require different diets at different stages of maturity. Vegetarian lizards need the right combination of vegetables, greens, and fruits. Certain vegetables/greens/fruits are good and some are bad so you can't just throw some veggies in the cage and hope for the best. You need to do the research.
What kind of reptile is for you? Obviously some reptiles would be better for certain people. It just depends on the amount of time you have and how devoted you are. Do you want a lizard? A carnivorous one? A vegetarian or omnivorous one? Can you pick up bugs? Size also should be considered. Will you be able to provide a large enough enclosure for an adult? How bout a turtle? Aquatic or terrestrial? What about a snake? Can you handle feeding mice? There a so many options when it comes to reptiles.
Remember... Whenever you buy an animal, you are not just buying that animal. You must take into account all the things the animal will need. So a seven dollar turtle might end up costing you over a hundred dollars after you've bought the tank, heater, fluorecent light fixture, UVB bulb, water conditionor, turtle food, dome light, and a vet visit. Please think things through. Reptiles can live a very long time.