Brood Wars is to Starcraft what Frozen Throne is to Warcraft III
I have already written a review of Starcraft on my blog and there are many other reviews about it on this site. The fact is that you have to play Starcraft first before you can start with Brood wars, since the story continues directly and the game is also harder, which requires you to use skills you have obtained in the first game.
Brood Wars is basically the same as Starcraft. Each race comes with 2 new interesting units, that shift the balance of power even more from one side to the other. Gameplay is basically the same as it was in Starcraft, the story is similarly interesting (maybe a bit more diverse and to the point), while the real "add on" of this game comes in the mission designs. Starcraft, like Warcraft III, had rather plain missions, most of them ranking in the "build and destroy enemy base" level. Some of the "walk around with a hero and destroy things" missions were thrown in just no to make it utterly dull.
Whereas in Brood Wars, similarly to Frozen Throne, the missions are interestingly and inovatively done. Most of the time enemy bases have their own exact characteristics to which you have to adjust in order to beat the enemy. Sometimes you don't even have to destroy the enemy base, but you just have to infiltrate to certain places.
Starcraft was interesting because it was something new and exciting, while Brood wars doesn't bring anything new in it's essence, but has more structured and intelectual missions, which also makes it fun to play.
Because the game was released only 8 months after Starcraft, the movement problem offcourse wasn't corrected. If in Starcraft it didn't influence the gameplay, I can not say that for this one. Brood Wars is harder, that's why it is far more frustrating when units keep bumping into each other, walk around stupidly, take extremely long routs around the map and follow one unit clumsily into the enemy base to get destroyed instantly. Not to mention the fact that units get stuck inside a cluster of buildings, even when they have an enourmous path through it. I have even seen a unit go through the building and then the exact same type of unit that couldn't go through and took a huge path around.
Thankfully this is the only mistake I have managed to observe.
The bottom line is that Brood Wars is the sequel of an awesome game, which brings us just enough of something new to still make it as awesome as it's predecessor.