The Renaissance is probably one of the nicest hotels in downtown Chicago. I have enjoyed their service twice now, and each time has been an excellent experience.
The hotel is probably five or six blocks from Magnificent Mile and a short hike to Millenium Park. The hotel has a constant stream of cabs to take you to more distant attractions and there is an El stop about a block from the hotel to get to and from the airport or out to other parts of the city.
Inside the hotel, the lobby is very nice. Service at the desk is as prompt as can be expected when there is a check-in or check-out rush. The concierge services were good when I used them in my previous stay.
The fitness facilities are quite large for a hotel (or at least many hotels I've stayed at) and all the equipment was relatively new and included free weights as well as cardio machines. It can get crowded as there are litterally hundreds of guests that could potentially be using it, but no worse than my normal gym back home.
Room service is prompt. The only issue I had was addressed quickly. They missed part of my order and the attendant must have had a cellphone on him to call down because it couldn't have taken more than 5 minutes for the rest to arrive.
The rooms, though, and specifically the beds, are what make the stay. The Renaissance beds are as comfortable as if not superior to the Westin's. The furnishings are in good order overall. The room sizes, however, vary slightly. Remember, this is a downtown room, so it may feel a little smaller than normal. My first stay had me in a smaller room. The second was in a corner room, which was definitely larger.
Given its location, service and quality of the rooms, it was worth the $200 I paid both the first and second times. You might be able to find a better rate booking further out, but closer in, $200 seems to be the price of entry (although it is not out of line with what you'll find elsewhere downtown).
Overall, I recommend this hotel completely.
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