A generator is one of those accessories that once purchased you will wonder how you ever lived without it. As stated by some others it allows for complete freedom from designated RV parks and enables you to get lost in nature without having to sacrifice luxuries such as fresh brewed coffee and AC on a hot night. It also offers piece of mind by knowing you have an emergency backup source of power.
That said;
Generators are not for everyone and if your camping style is a little more rough and ready you can definitely get away with omitting the generator.
If you do decide that a generator is a purchase you would like to invest in I would highly recommend checking out
http://www.quietpowergenerators.com/ to find the right generator for your specific needs. They have a
usages chart page that allows you to calculate what size generator would best suit your needs. It also has a bunch of helpful general info as well as some very detailed reviews.
Hope this helps in deciding if a generator is right for you! All the best,
Dave