How have I never written a review here before? Outside of my own place, this was the place I've been to the most in Toronto by far.
The good: It is the hub of Toronto. Go train, Go bus, and TTC all connect through Union Station. If you need to get anywhere downtown by subway, or if you need to get anywhere around the GTA and beyond, chances are union station has a connection that will get you there somehow.
The bad: It is old and stinky and crowded. During rush hour, it is a mothereffin circus. Definitely could use a face lift, although they shouldn't get rid of the beautiful architecture. I think they are in the middle of cleaning it up now. It can get a little confusing moving about. Needs a navigation app and better display maps and signs.
Overall: Gets the job done. Barely.