Have stayed at the Denver Marriott City Center 3 times on business and have been consistently impressed. Good quality business hotel.
On arrival, checkin was smooth and efficient. Front desk staff was friendly. Overall, service at the hotel was very good.
On each visit, I've been upgraded to an executive king. Basically, it's like a normal room, but with extra space -- which is nice. You don't spend all of your time trying not to bump into things! Beds are really comfortable. Rooms are clean. Bathrooms are a little crowded and somewhat dark. It does the job.
Concierge lounge is where this property shines. Breakfast includes scrambled and hard-boiled eggs, bacon or sausage, hot / cold cereal, fruit, etc. The coffee is really good. The staff is very helpful and friendly. In the evenings, they do veges, cheeses, cold cuts and canapes. Two of the 3 weeks I was there, the did a managers reception in the lounge on Wednesday evening with a "specially selected menu" . There were more hot options, and free flowing beer and wine. Many of the managers were there mingling with the guests. It's a nice touch when so many are cutting back. Also, many of the Marriott properties have gone to cookies only for dessert. This property still has really desserts -- whether it's mini apple pies, nice cakes, tarts, etc.
Location / Transport
Property is a block or two from the 16th street mall, so it's very convenient! Cabs are readily accessible. Only item to note -- downtown is FAR from the airport. You're looking at almost $55 from the airport to the hotel and $51 going back.
Only thing I'd mention is this. Elevators tend to be really slow --- especially first thing in the morning and at the dinner hour. You have to plan accordingly.
When I'm in town, this is definitely where I'd choose to stay.