Union station is a beautiful place... mostly. It is not only the busiest train station in Canada, but the busiest transportation point in Canada - its more busy than Pearson (!).
Unfortunately a very small margin of these people actually come through the nice part, as most are GO Train riders and therefore end up in the dark, noisy, smelly, ugly, chaotic commuter hell of the GO concourse. Some find their way (as its fairly easy due to the disjointed and confusing nature of the train shed/platform to ticket/exit area connections) to the VIA area (the really nice part). The subway also comes here. its station is another commuter hell, part of the reason why this station is under Perma-Construction, I don't remember ever seeing it without some form of construction. both GO and the TTC are making their parts tolerable, and the train platforms are being redone so that some sunlight comes in. the whole station is covered in scaffolding, Front Street is completely dug up (again) and to get to street level you have to walk up these sketchy temporary stairs (along with the rest of the financial district) that feel like they are about to collapse.
An annoying thing is that if your at either end of a GO train and you come in on the outer tracks (think 10ish to 25) then you'll have to walk out into the Bay/York Street tunnels.