I tried VATSIM, but maybe I'm just too lazy. I don't feel like going through the training they have. I already know what I'm doing.
Computer sims are sure fun. I never tried ATC2, but have spent hours playing ATCC and love it. However, VATSIM is still something different from an AI simulator. You'll need a much greater knowledge of the ATC procedures and phraseology to work VATSIM traffic, because the types of flights vary greately from one to another, and you'll often be dealing with traffic to multiple airports 400 miles away.
Don't let the previous experience discourage you, and give VATSIM another try. There's a whole lot to learn to work VATSIM traffic, and it will actually make you a better controller. It can be as difficult as an enjoyable process, and can get you addicted easily.