My fiance and I took this underground train to and from the Olympic Stadium and Biodome back to a station within a mile of our hotel. The STM is just another form of transportation similar to the San Francisco Bay Area's own BART.
The system is efficient, convenient, and it is very easy to figure out, even if you don't know any French. I would take the STM again because you don't need to hastle with finding parking space in town.