Perfect location for a quick weekend.
We visit Chicago often and have stayed at many other Marriott properties in the city, but this was our first time at the Marriott on Michigan Ave. We stayed in the king bedded room and had a rate that included self parking for $31 per day. We normally do valet in downtown Chicago, so were pleased that the self park at this property was right across the street, was very clean and well lit. While my spouse parked the car, the bellman helped me with luggage and check in- service very polite and speedy. 
We were there for a shopping weekend so this was a perfect location with a lobby entrance right on Michigan Ave. The subway is only a few blocks away, cabs are plentiful- but plenty of shopping is within easy walking distance. 
The room itself was smallish, but not terrible for two people. My only complaint about size was the bathroom- wow. It is seriously tiny. No room for two people, and the door barely clears the front of the toilet when closing. For a quick stay that is not an issue- and all was clean and well supplied. Bed and pillows were very comfortable. Turndown service was a nice treat and unexpected in such a large hotel. 
Overall we had a good experience. I would return and/or recommend for location and quality. If you are looking for a more intimate or luxury experience, consider the JW Marriott in the loop instead.