I don't think it takes any more skill than holdem, nor is it really more complicate, per se. It's really that there are more ways a given hand can win and it's a bit harder to estimate your odds. That is, it's not more complicated because figuring your odds works the same way as in holdem, but the depth involved is greater. That said, I don't usually play Omaha because my mind is simple, so I have enough trouble keeping up with the odds in holdem. But I hear there is money to be made in O if you can stand the donk variance over the long term.