The section of the barbarian highlands that we saw made it look similar to some of the forest lands from Act I in Diablo, but with six subquests in the chapter, there is room for more visual variety. Some of the screenshots we've seen reveal icy areas and frozen waterfalls. But by far the most remarkable thing about the highlands is the epic war raging throughout. The highlands will feel a lot more dangerous and active thanks to the raging battles, and players will have some interesting new monsters like the Overlord, Dragon Razor or reanimated hordes. There are also siege weapons like catapults that pin down your player with death from above -- but fortunately those weapons can be destroyed with a few hearty blows.
Obviously, players will need to be pretty high level if they are going to follow Baal into the fifth act. DII veterans can use their characters from the single-player campaign, or they can restart and play through the whole of DII again as one of the two new characters -- the assassin or the druid. Both characters are still being tweaked and balanced right now, but both have interesting attacks that distinguish them from the five DII regulars.