I never like to play the last two or three round because of how they drag, but until then it's a full-day's worth of fun. Edit: Not really my sort of game anymore, but fond memories keep it high in the rankings.
Samarkand is great either way, but I give the nod to this very minor expansion, mainly because it adds a bit of variation from turn to turn, and it lets you avoid the issue of what happens when you want to sell only two units of a depressed commodity.
Not so good for me, since I like to play with a timer and many of the options just can't be worked with a timer. A few of the boards are fun to use though, so it's not a total waste of an expansion for me.