Civilization IV promises to be remembered as an enduring turn-based strategy masterpiece.
The Bad: It's sometimes difficult to take cities, especially with unit promotions, multiplayer server browser's a little rough
Civilization IV is the latest game in one of the most venerable gaming series of all time, and although I can't tell you whether or not it's the best game (sadly, I never played any of the previous games), I can promise you that Civilization IV is a game of such immensely high caliber that I doubt you will be disappointed.
Civ IV is of course a turn-based strategy game in which you take a civilization from fledgling status and finally, fulfill one of the many victory conditions to become the most powerful civilization in the world. This can be done many ways, which adds a lot of depth to the game's overall arc, but each game's small decisions add a lot of variety. The great thing about this game is that barely anything is rote, mechanical boring stuff - you spend your time only with the big, important decisions that will have a palpable impact in this game thanks to Civ IV's interface. This means you will practically never get frustrated with this game because of it being boring, especially since your turns pass quickly and it's extremely easy to locate all the information in Civ IV, a considerable amount of which is presented in the new 3D board visually. Everything is accessed easily by a simple click or two. This is good, as by the end of the game you will have a LOT to manage, but it's always fun.
The game is balanced superbly. Each unit when committed to combat now has a single power rating - the higher, the better. However there are lots of other factors - certain tiles will offer more defensive protection than others (especially cities), and once a unit gains enough experience (i.e. kills enough other units) you can give it a promotion. While you can always give your unit a generic +10% combat promotion, other promotions are much more valuable if you use them right. However it's an important decision to make, as each unit is then specialized. Although you can always use a unit that gets better defense in the woods as a city attacker in the plains, it would essentially negate the promotion that you spen the unit's experience for. The only downside to this system is that promotions occasionally seem a little drastic, such as when an archer beats an axeman. The only other problem is that used correctly, this system can render some cities nearly impossible to take no matter how many units you throw at it. This is because the bigger cities will add a defense bonus, plus you can fortify units over a series of turns (you gain 5% each turn, maximum fortification bonus is 25%), plus many units can be promoted to become better city defenders. Otherwise though, it's a terrific system that adds a lot of depth to your maneuvers.
The graphics are about as good as they can be in a turn-based strategy game, with a beautifully animated and a lively 3D board. The sound is great as well, with a great score (the opening music is particularly reminiscent of the Lion King, which has been commented on many times) and nice sounds to accompany the combat animations. The value is nearly limitless, with flawless single-player action and finally, highly functional multiplayer. The multiplayer is constructed to allow for players to join and leave midgame. While this has the negative effect of a true game rarely being played out, it's mostly positive, as people will often have to leave because they're doing bad (the AI will take over). The multiplayer server browser's a little rough and annoying though, as it's constantly refreshing as you go instead of staying static until you tell it to refresh.
Ultimately, though, Civ IV easily overcomes its flaws to become an enduring strategy classic. If you have an even remote interest in strategy, or perhaps a fondness for board-games, and ESPECIALLY if you're a fan of the previous games, get this game. Now.