Okay, so Civilization IV is the last game of the worldwide known strategic serie : Sid Meier's Civilization.
This is pure strategy, if you're not sure you'll like, I'd say that you shouldn't. But if you like strategic games, simply run to your nearest store !
This is non-rts. Means you play each time it's your turn. It may look a little bit slow and devours a LOT OF TIME. Seriously, I noticed that I usually made my first army fight 2 hours after I started playing.
Civilization is also not known for graphics, but they made efforts this is obvious. But seriously, we're not looking for graphics when buying a Civilization, aren't we ? :P Sound is great like always (real classical known musics)
Now, the strategic part. It's simply awesome ! They added so many possibilities that I couldn't list here. Anyway, you can now choose perfectly your doctrines. The alliance options are like infinite. Diplomatic side is incredibly great. You can now make really interesting trades with your buddies.
The last positive point is the map/mods editor they made. It inscreases so much the gaming durability. You can now find on the web many more maps.
Conclusion : Buy it if you like Civilization games or pure strategy, otherwise, you might be disapointed =)