You definitely need to give yourself more than a day to see this museum, which was our mistake. We showed up here around noon on a weekday and they closed at 5:30 p.m.... we didn't have enough time to see everything.
This place reminded me a lot of the Chicago History Museum: there were a lot of artifacts and objects from Ontario's history as well as descriptions of major events and milestones in the establishment of Ontario and Toronto by indigenous settlers and colonists. Be prepared to read a LOT of narrative. I think this is one thing some museums do poorly and ROM is an example of that exactly: there is so much text to get through to learn about one portion of an exhibit that it's exhausting to try and read everything. Museums do better if they get a good amount of audio, video, and text so people don't feel like they have to spend their day reading a novel just to get some history. If i wanted to read a novel, I would have just picked one up instead of coming here.
Other than all of the text, there was a lot of cool stuff to see, especially about the geographic changes of the land, the movement of indigenous peoples, and the settlement of colonial villages. As you go upstairs, there's special exhibits that get closer to the modern day. The top floor was my favorite: a look at gambling, gangsters, and prohibition in Toronto. It was a fun, interactive exhibit that combined audio, video, and text with interesting visual setups and artifacts from the era. Definitely not something I knew about Toronto's history and I was eager to go through each part of the exhibit.
Prices were a bit high and there were no discounts for students, non-residents, foreign travelers, etc. Worth paying but feels a bit steep. I'd definitely come back to check out more and read some of the things I wasn't able to get to in my traveler's fatigue.