Location, room size, breakfast buffet
I stayed for several nights through a major national meeting which was at McCormick Place. 
The location on the Magnificent Mile, the suites and the buffet breakfast, which caters for different national food preferences, were great. 
If there is a downside to the hotel, its the logistics of getting in and out.
The hotel has a relatively small street frontage and the entrance is a little clumsy with people milling around inside and outside the door. There is limited space for taxis act at the front. The lobby itself has a coffee place that sells sandwiches and drinks to go and some seating. 
The in/out issues were evident when on the first morning, I needed to get to McCormick Place early. Allowing an hour, I rounded the corner to the conference bus in front of the Westin, to find the queue extending well up Michigan. I returned to the Hotel and asked for a taxi - they have a lot of trouble getting taxis to come in busy times. I eventually got picked up by someone in taxi headed to McCormick. 
Message: if you need a taxi - reserve one ahead.