I stayed for 6 nights and the staff are incredibly friendly and helpful. But the hotel itself is a bit run down with older rooms, older beds, fixtures, etc.

The executive lounge is nice but the gym has older equipment some which did not work properly. Because the staff were so terrific I wish I could say that I will retune but until the hotel is upgraded, I recommend staying elsewhere.

The beds are very hard as well and I was unable to cool my room down enough to my liking. It was "heat only" option

The food in the lobby restaurant was good.

Stayed at the hotel for 30 days on a business trip, and all the staff was great even if all if them didn't understand english that well, thye would find someone who did to help you.
All the staff in Club lounge are great, after the first week they knew what tea and breakfast I prefered, and I had it on my table without even asking. They were also great with helping me to arrange trips. My room was spacious enough, and I loved the huge bed!

I stayed at the Renaissance Beijing twice - for six days in May 2011 and five days in June 2011 and was really pleased with the experience. The rooms were nice, the service excellent and I had no complaints during my visit. To be fair, I did not have lunch or dinner at the restaurant.
Free internet if you are a Marriott Rewards member. No? Enroll on-line before you travel to China.
A nice advantage is that the hotel is just off the 3rd ring road and is a quick ride to and from the airport. Be sure to take directions to whatever hotel you are using (in Chinese) because the taxi drivers sometimes say they have not clue where to go. Ripping off tourists is common. A taxi from the airport to the hotel reviews is about 70 rnb.
Have a great trip!

Stayed here recently for a night.

While the hotel is fine, its certainly nothing special. I think other folks' reviews have nailed some of the key points:
- The room itself was spacious and well appointed, though it showed some age. It was pretty clean, but not spotless. I didn't, for example, take a bath, just because I had an "eh" feeling about how well it would have been cleaned.
- There's a funky odor in the hallways that permeates the room. Honestly, its almost urine-smelling, which is pretty offputting.
- The restaurant was ok, but again, nothing special. Walk across the street and eat at Kro's if you want western, or Bellagio.
- The bar is equally "eh" and service was weak.
- Like most Marriott's, you have to pay for internet (which is ridiculous) and there's no wifi.

Bottom line is that its one of the weakest Marriott properties I've stayed at in China, and you can absolutely do better in Beijing. Unless you were hellbent on being in that particular area, I really don't think I'd recommend this hotel.