If you're interested in Avatar, I would recommend that you go and read Shalineth's review, second from the bottom of the review list as of now. Note this part:
"All too often, an entire group would be 3 Warriors, a Rogue (maybe) and Cleric to heal the 'Tank'..."
They've taken steps to change that, but in over a year since that post was made, Avatar is still like that.
If you want a powerful character, make a rog or a war. If you want to be the best hitter but don't mind being a second-rate tank, be an archer. If you want to be a good tank but don't mind being a second-rate hitter, be a monk. If you don't care if your character is weak, play any other class.
They did put in some changes to help this, and it's taken them a long way, but they still have a long ways more to go. When I made my character, a year and a half ago, warrior and rogue were the only classes that weren't marked as hard to play. (Archers hadn't been put in at that time, fyi.) This doesn't mean that other classes are more complex but still as powerful, it doesn't mean that they have a weak point that counters a strong point, it doesn't mean that rogues and warriors are easier to start and then things balance out. It means that rogues and warriors will always be more powerful, and people will be reluctant to group anything that isn't a rogue, warrior, or archer.
If you like that in a mud, Avatar is great for you. A lot of people seem very happy with it. I wish I would have known about this before I put so much time into Avatar. There's a lot of important things about Avatar that I didn't find out for some time, and I think it's nice to make information like that available to new players.