Despite the fact that my level 70 Hunter isn't technically my main, she's probably my favorite character. A lot of people will tell you that a Hunter is an overly easy class: sic your pet, turn on Auto Shot, and you're done. While having a built-in tank that you can even heal a bit gives you a pretty strong advantage when going it alone, I'd have to say they oversimplify things a bit.
The largest area where the complexity of the Hunter class shows is in end-game DPS. If you want to be the most effective DPSer possible, it takes quite a bit of work. The way that you must weave shots in between your auto shots is a complicated dance that requires split second timing that can mean vast differences in DPS totals between Hunters. Cheeky of the Khadgar-US server (author of the famous Cheeky's Spreadsheet) posted a very concise and well-stated summary of some of the problems with Hunter DPS on the official US forums here a few months back. The post was originally written by Lactose of the Talnivarr-EU Server, who posted it on the EU forms here, where it got some blue love
today a while back.