If I could plant only one thing in the vegetable garden, it would definitely be green beans. I love them. Love everything about them. They are so easy to grow. Make a row, drop in seeds, add water. Voila. A few short weeks later you've got beans. I think that's part of the appeal. I'm not the most patient person, so quick turn around is a great thing in my opinion! I get excited when I see them germinate, excited when I see them start flowering, and really excited when I realize it's time to harvest!
They produce like crazy, and when they really get going you have to harvest every single day. That's pretty convenient, because I could eat green beans every single day! I've experimented with different varities of green and yellow beans, and I love them all. Last year I grew a variety of haricot verts (ooh la la!) and they were really good. This year I am growing Tenderettes and a variety of yellow wax beans I have had for a few years (but can't remember the name).
I even think the plants are so pretty. They are fairly disease and pest resistant, although some years I get some Mexican bean beetles or stink bugs. It's hard to prevent stink bugs, and usually the plants are hardy enough to tolerate the pests without any pesticides (which is good, because I really, really try to avoid using any pesticides).
I just planted a second row last night. More beans on the way!