I've been playing SimCity a fair bit since I got it a couple of weeks or so ago, and have found it pretty fun. Single-player private regions can be quite good, given the need for city specialisations, creating a lot of switching from one city to the next to get all your ducks in a row. In the region I'm currently playing, I'm up to about 8 cities, with two great works completed. I think there are two more great works sites in it, so I'm aiming to have all four different great works up & running in it. The only thing that annoys me slightly is that each great work only seems to affect the subset of cities that are directly linked to it, rather the entire region, even if there are road, rail & ferry connections to other cities. Other effects are regionwide (e.g. city hall annexes), so it's a bit lame to not let the great works affect the whole region. It would unbalance everything, but still, it would be fun.
The bigger issue is the server lag between doing something in one city, and the other cities picking up the effect. This seems to have improved recently (in the same update that finally reactivated cheetah speed), esp. with regard to great work sites updating faster, but things like donations of money are still susceptible to significant delays. I've a couple of cities that generate many millions of simoleans per day and I want the cash to subsidise others that are running deficits, but it can take time for the cash to transfer.
Still, the game remains a pretty good time-sink.