A fairly entertaining city sandbox game, but it doesn't seem that different from SimCity 2000.
Since SimCity is a sandbox game there isn't a storyline, so I'll get right to the gameplay. SimCity 4 is a bit like SimCity meets The Sims. When you first start up the game you're looking at a game world called a region that acts like the Neighborhood system in The Sims. You begin by selecting a lot, and then using "God mode" to modify the terrain, plant trees, throw in some animals (though this is pointless as the animals seem to disappear after you exit God mode) etc.
After your terrain is to your liking (and do make sure it is, as you can't reenter god mode as it was once you leave it) you get to enter the largest part of all of the SimCity games - the Mayor mode. The Mayor mode is basically what SimCity veterans are used to. There's very little difference between SimCity 2000 and SimCity 4's Mayor mode (of course all SimCity 2000 had was a mayor mode). You begin by naming the city, and entering the name of the citys Mayor. You then place residential, commercial, and industrial zones to attract people to your city, then you provide them with power, water, educational services, and of course public safety services such as police, fire fighters, and doctors.
Like the past SimCity games you have to keep a close eye on your budget, obviously you want more income than what you're spending monthly. This is a bit easier in the latest edition of SimCity as you can more effectively restrict money demanding services so that their funding isn't way more than it needs to be.
There are of course a wide range of disasters if you feel like seeing your citizens suffer you sadistic monster, you. From giant robots, to UFOs, and the traditional tornado you can destroy the cities you created as easy as the click of a button. Also random disasters (mostly fire) occur, and unlike SimCity 2000 you can't disable them.
The newest feature in the series is probably the "My Sim" mode where you can import Sims from the actual "The Sims" game, and have them comment on your city. This is just a gimmick, though, as it doesn't really offer you anything new that your advisers won't tell you. Another gimmick is the "U-Drive it" option where you can drive around doing missions in your city in a style similar to SimCopter for SimCity 2000. Unlike SimCopter, however the U-Drive it mode is isometric instead of full 3D. Very disappointing since SimCopter was clearly their inspiration for this feature.
The graphics serve their purpose. Buildings, and civilians are still 2d, but they cast shadows, and there are clouds and a very nice lighting system in place. If you have mountains the bottom of the mountains, and some of the sides will be dark because the sun is not reaching it. This is a very nice effect, but for the most part the graphics are fairly average.
The audio is okay. The music is fairly decent, and the sound effects work, but the voices are the ridiculous language created for "The Sims". That worked in The Sims since they obviously couldn't record every possible sentence in English, but in SimCity 4 it's pointless.
SimCity 4 is a fun little sandbox game for people who always wanted to develop (and maybe destroy) their own city. Or farming town. Or whatever. Veterans of the series won't find any great new features, as they all seem to be gimmicky, but if you're a SimCity addict, and want better graphics for your city building then SimCity 4 is a great investment.