Warcraft III the Frozen Throne is not a major improvement on Warcraft III Reign of Chaos.
The only major improvement would be in the campaign which has now introduced a new unplayable race which plays a key role in the story.
Some minor improvements that make a small impact include, lower and higher costs to buildings and units, new units, a slightly higher food cap and minor changes in the human race to make another unplayable race (not the one i mentioned earlier) the blood elves which to me are just humans with long ears.
It is again an awesome game to play from the warcraft range and i have no doubt that anyone would get bored of playing it.
I would recommend it to anyone who wants to play it and to those people who think that getting the expansion of this game or any game is not worth it.
10/10