The W - City Center is a very nice hotel. The location is easy to reach from CTA, it's convenient to downtown businesses, and there are plenty of restaurants, bars, etc. nearby to keep you busy. The rooms are gigantic and easily are the biggest I've seen in a non-suite hotel.
I find that there are two types of W's. The first type is an upscale hotel with a club feel and the second type is an upscale club that seems to double as a hotel. This hotel is definitely the second type. That's not necessarily good or bad, as everyone has his or her own preference, but FYI.