For me, this is the best game ever created, regardless of genre.
I was a kid when I first played it, so I never actually considered it an economic strategy. For me it was all trains and planes (never liked trucks) and trying to develop a city as much as possible (24.000 people in one city was my max). I never played with competitors and probably my favorite times were finding that low pass in the mountains, or changing old tracks for maglev ones. Or seeing those silly futuristic cell buildings and thinking "Yey, soon I'll get the Concorde". Or putting my HQ in the middle of a lake and linking it with the best money can buy bridges.
In fact, all this writing has just convinced me to play another map...