I think it is a great system. Soon teams will stop wasting it on 50/50 calls and only use it when the decision by the umpire is a true howler. The LBW review from the bowling of Harris was the worst I have ever seen.
Needs to be made mandatory for all Test series. It's a farce that some series have a completely different set of rulings. Can you imagine games being played without the third man for run-outs? I don't care what it costs, the ICC runs enough pointless tournaments to bank for a good idea.