The frozen throne is an expansion of the popular game - Warcraft 3 (see my previous reviews for more information). The expansions includes a new hero for each race (that's four in total) and a couple of new units of each race as well.
More importantly the map builder has been updated. Meaning the quality of custom maps coming from TFT community far super seeds the Warcraft 3 team. Sadly more people now play the expansion than the original meaning that you're almost forced to upgrade if you want to play online. (You're still able to find games in warcraft 3, just not as many).
This is a must buy if you have the original - while it was a bit more pricey it's a worth it if you plan to play online. (I am unsure of why it was more expensive than the original. Doesn't make a whole lotta sense to me.)