Part of the appeal is that the reverse side of the board is Berlin, Germany/DE (as opposed to Manhattan), which is where my oldest daughter was born. 🙂 Some other appealing factors are that according to a Video on BGG, some of the tiles are transparent (except for a colored stripe for the players particular Ubahn line) and can be stacked on top of one another, without obscuring the tile beneath it. The railcars are plastic on top and metal on the bottom, and the Meeples ride in 'em. 🙂 The boards have recesses for passengers and stations to help keep the pieces in place. I like the engine-building and pickup and delivery aspects of the game, too.
That reminds me of one of my games that's less "modern", Flightplan (1985). Meeples ride in the planes, as you transfer your passengers to and from different airports.