I've been playing Simcity from its inception. Simcity 4 is by far the best installment of the series. It has really changed quite a bit from SC3000. The ability you have to manage and design your city is extensive. Definitely pick up the newest expansion if you decide to play it, it adds so many options to transportation that have never been in Simcity before. All your services are localized now instead of serving the entire populous. There are dozens of tools available as well to assist you with various desicions you'll have to make.
The new terrain and region maps are gorgeous. You'll get some extremely life-life mountain ranges, rolling hills, or carved canyons with the newest terrain editor. Importing geographical data is a great way to build off actual terrain from any part of the world. Having all of your cities react to each other from within the region takes some getting used to, but it allows some really expansive customization options for your area. You could end up having a city of only residential, and still be pulling in some serious cash and growth. All because your commercial and industry is only a city away.
If you were a fan of the series at all, pick up SC4. You won't be disappointed. Also stop by
www.simtropolis.com and check out their mods and community forums. The mods people have made can really change the mechanics of the game, sometimes as cheats, sometimes as just improvements to the game's functionality.