Homeworld 2 is a major disappointment all around, unless you want some great eye candy.
Lets start with the single player campaign and its story. The story takes place a while after the end of the original game. The Higarans have settled on Higara, have rebuilt their empire, and have decimated their rival: the Taidani (I don't think I spelled that right...). Ah- but wait! Their troubles aren't over- for a new foe has shown up to bring the hammer down upon the Higarans! The Vaygr suddenly show up and start cutting a brutal swath through the Higarans empire. So basically, the campaign focuses on the mothership's attempt to stop the Vaygr from taking over Higara. Its unfortunate that the story here is as weak as it is. At least the quality of the scenarios themselves is at least as high as it was in the original, so no real complaints there. But alas- the campaign is hampered by Homeworld 2's lackluster gameplay.
Why is the gameplay so disappointing? The answer is simple: Homeworld 2 does absolutely nothing new with it. That and the fleets in Homeworld 2 just aren't as varied or fun to use as they were in the original. Also, the game's ship formations are extremely limited compared to those of the original. So if anything, Homeworld 2 simplifies the original's gameplay for the worse.
For those who do still enjoy Homeworld 2's gameplay despite these issues will undoubtedly be impressed by the game's visuals, which are excellent. The ships are all extremely well detailed, and the trails made by corvettes and fighters are satisfying to look at. The only complaint to be had is that the ship designs are less inventive that those of the original Homeworld, but this is a minor complaint. The game however suffers in the sound department- with some iffy voice acting- especially since every ship shares the same voice. They should of given each ship a unique voice over, just like in Cataclysm. The other sound effects are similar to those of the original, but darn it- those ion cannons don't sound nearly as satisfying anymore!
In the end, Homeworld 2 was a major letdown by Relic. Especially with the base game they had to work with, which was great. Relic SOMEHOW seriously messed up with this one, so ultimately, Homeworld 2 can only be recommended for fanatics of the original game.