It is a very good game. There's only 4 cities but there's plenty of scenarios and tasks in each of them. It's also not an easy game - you won't end up with billions of pounds if you are making a success of your company unlike in most other 'tycoon' games so you're always thinking about budgets and whether you can actually afford to replace your fleet or build that new line.
The downsides are that there's not a huge range of vehicle types - you're limited to buses, trams, metro, ferries and (oddly) helicopters, so no trains (though there are railway stations that you can link up to). I also got a little bored of the game recently, but that was after several weeks playing it, and maybe the new expansion packs may perk my interest again.
Overall, well worth the money.
