The weight room/fitness areas are great, too. I wish there were more basketball courts, but with the Field House there isn't much need to add that currently. The second phase of the rec center will include basketball courts, as well as racquetball/squash courts. There isn't any date set for construction to begin on that, though; it's just what they'll do when they inevitably take out the Field House for hospital expansion down the road.
The natatorium is definitely the crown jewell of the facility, though. The building was completed in the fall of 2010, and I think it's already hosted the Big Ten swimming championships twice (one men's, one women's) and this past year's NCAA men's championships.