What do you like most about Korra that you think make it a great show, one probably even better than the original Avatar the Last Airbender series?
For the same reason Zeta Gundam is better than Mobile Suit Gundam. It's more developed, in terms of themes and plot. It has more substance to its narrative, goes in more interesting directions than the previous show. Both are good, mind you, but Legend of Korra just feels a little more evolved.