Union station is one of those places that makes me realize I'm visiting a big city. It can be a little confusing, perhaps a bit overwhelming, but it's awesome for many, many reasons.
Do you like to people watch? This might be the best place in the world to do it.
Need to catch a train? VIA? GO? TTC? They are all here (which again, can make it a bit confusing)
For the most part, it's clean. Sometimes there are people begging for change, but they tend not to be a nuisance. There are various food vendors too, if you are really in need of a bite to eat between trains.