As a frequent user of this train station back in '06 when I was living in QC I visited this station at least eight times that year.
As a rushed traveller, I never took in the train stations' beauty. On on a recent visit to the 514, I spent sometime here. Gare Central is the Cadillac of train stations in Canada. This place is gorgeous. It's expansive and airy and a truly beautiful building. Take a moment from your commute to x place and take in how pretty the space is. Beyond that there are tons of places to eat - Montreal does food courts well and Gare Central is no exception - poutine, lots of ethnic options, Mickey D's and a few healthy choices as the station is connected to the underground. There are quite a few shops as well to keep you busy if you have some time to kill - notably a giant Bureau en Gros (Staples), SAQ (liquor store), Carleton Cards, Bentley and even a dollar store.
Seating isn't great if you have a some time to kill so I recommend getting a beverage and a snack at Second Cup. Lots of place to sit, people watch and a killer vantage point of the train schedule. All aboard please.