I'm rarely able to get into 4X games, but Galactic Civilizations II is just plain brilliant.
While sequels are generally continuations of a sort, the only way in which GC II fits this is the campaign which is essentially a waste of time. Players are better off playing the game the way it was meant to be played via the standard "New Game", or "Metaverse" functions. In a standard game you're able to select your galaxy size, star amount, habitable planet amount, victory conditions, etc. and then select one of ten pre-defined races and customize them, or create your own race to play as. Once the game kicks off your race starts out with just its home world, and a survey and colony ship. With these tools you have to explore the galaxy, and colonize new worlds thus expanding your Empire, and meeting new major and minor races along the way.
One of the beauties of this title is how you can win the game in one of four ways. You can go the old fashioned way and either commit genocide by wiping out all other civilizations (or merely conquering them), spreading your influence and gradually manipulating alien worlds to join your empire, becoming the head of a Coalition by forming an Alliance with every major race, or unlocking the mysteries of the universe and ascending your race to Godhood. Since most of the game is complex, achieving any of these conditions can be quite challenging especially on high difficulty levels.
Combat can be considered solid, but not exceptional. Essentially it comes down to battle of the stats. Space combat places emphasis on ship attack, and defense... naturally. Since GalCiv II comes with a ship builder you can create your own starships with the technology you research over the course of the game, and this is encouraged since the pre-built starships are pretty mediocre. Land combat is fairly straight forward, and deep enough not to be considered a cakewalk (except on the cakewalk difficulty, of course).
I did have some issues with the game. Navigating the galactic map can be cumbersome the larger it is, for example the largest map size (Gigantic) is quite tedious to navigate through. Mouse scroll is slow, and the minimap zoom isn't particularly helpful. Also the game tends to crash out of the blue between turns, fortunately this rarely happens and the game autosaves every few turns making CTDs little more than a minor inconvenience. One last complaint I have is the inability to customize AI races. You can create your own custom race to play as, but the AI has to use the stock races which is disappointing.
Visually GalCiv II isn't too impressive, but this is first and foremost a large scale TBS title, so that's understandable. The graphics aren't bad by any means, it's a full 3d game meaning that space battles, and the galactic map aren't too bad to look at for modern gamers. Audio-wise the game is so-so, some of the music is good (the menu theme, and a couple of the peace-time in-game musics), but most of it isn't anything special. There's no voice acting, and sound effects are rare.
Galactic Civilizations II is worth playing even if you may not be into 4X strategy games. It provides a lot of freedom, and is definitely deep enough to be a breath of fresh air in an industry where things are becoming more and more streamlined.