Although I didn't spend too much time in Montreal, I was on the Metro just enough to get a few impressions of the city's main transportation spine.
One of the best parts of Montreal's Metro can be seen from the street. Every station entrance is well-marked with the iconic logo of the system, the arrow pointing down with a circle around it. Although it seems like a simple touch, there are plenty of cities where this is not the case, and knowing where to board the train helps out, especially for visitors.
The trains run on rubber wheels instead of the typical steel ones, but I really didn't notice that much of a difference. Trains bounce from side to side just as much as those in Boston or New York, and the same electrical tones emanate from the station as the train leaves the platform. The only difference that I could pick out is that braking and turning are somewhat quieter with rubber wheels.
One of the gripes I had with the system is the fare cards. A day or month pass consists of a very flimsy, extremely thin plastic sheet about the size of a credit card. This would be fine if a small chip didn't have to be housed in there. The chip inside the card can be bent even just by putting it in a stuffed wallet, and the refund system for these involves having a five-minute argument with a station employee, then receiving a free-ride ticket, valid for one ride, as a refund.
The other problem I encountered was the absurd lack of decent transportation to and from the main airport. Although the airport is fairly far out of the city, service consists of a small bus that runs every half-hour. Like any other bus, it is easily stuck in traffic and pretty slow.
Other than that, I really enjoyed my time on the Metro. It's a mostly great system for a great city.