Having stayed in the Marriott for over a year and a half, you would think that I'd know this place like the back of my hand, but I don't.
There are some dishes that are always good, but the over pricing and mediocre food is enough to motivate me to leave the building for dinner.
The thai chowder is great and their tapas are pretty solid. The salmon is also well prepared, but that's were the good ends.
Sometimes the service can be very slow for no apparent reason and seems to vary by waiter. The food is over priced for what it is and I would much rather walk over to The Keg and get a similar dish for less. Another issue is the price of the drinks. A double Johnny Walker Black on the rocks, for example, will set you back $20!!!! I order this quite a lot and can honestly say that is the most I have ever paid for it in Montreal. The same drink will cost you $14 maybe at The Keg or anywhere else.
If the weather outside is frightful, or if you REALLY don't feel like going to any effort for dinner, Le Senateur is much better than room service. But in comparison to places within walking distance or accessible by the underground paths, it is certainly worth the 10 minute walk.