I have stayed at the STL REN a few times in the last year. Hotel is pretty nice and the rooms seem larger than the STL Marriott. Decent lounge, nice restaurant/bar. Great staff.
Lounge closed on weekends but you get full breakfast. Choice of points or coupon for food at Plat gift. Like the Marriott, they charge for parking, but the gates never seem to be in use, so it did not seem to be enforced.
Not much in walking distance. 3-5 minute free shuttle ride to/from airport.
Wife and I prefer the REN over the Marriott at STL due to nicer rooms/ambiance.