This is a great way to get an overall view of the 'city highlights' if the guidebook has left you scratching your head when making a 'Must See' list.
The Tram Turistico is a restored tram from the 1920s, which rolls around the central districts of Milan making its way past the city's highlights. For EUR10 each we were entertained for 1.5 hours. We would have been even more eager to listen and be entertained had we not woken up at 5am to catch our flights to Milan. That combined with the rhythm of the tram and the day's heat left us both a bit drowsy. *sheepish grin*
Our tram ride started outside the Sforza Castle. The ticket allows you to get on and off at any time all day, along the route of the city's sites. This is as long as the tram is still running and only for the day the ticket is valid for. So, if you're spending a day in Milan, this would be a good option. The subway is cheap (EUR1 for 75 minutes) but this affords you the luxury of not having to buy a guidebook if you're only in Milan for a day.
As we rolled along the different sites (Piazza Castello, Duomo, Colonne St. Lorenzo, Darsena, S, Maria delle Grazie, Via Albricci, Porto Venezia, Piazza iv Novembre, Piazza Repubblica, Manzoni, Piazza della Scala, Ponte Vetero) we each had headphones, with recordings in the language of our choice (English, Japanese, Spanish, German, Italian and French), pointing out the sights and their history.
The only downside seemed to be that sometimes 'right' was actually 'left' - so you may want to memorize pictures beforehand to identify what you should be looking out for, although descriptions are given along with a routing map. Also, the windows were thick and pretty high up, so leaning out the window was the best way to get a good picture. It was a bit of a bumpy ride at times (jerking to a halt) but that's part of maneuvering in Milanese traffic.