Priority Pass (a lounge-access program), which is free with the American Express Platinum card, gives cardholders access to the KLM Crown Lounge in Houston regardless of airline or class of service. I visited the lounge a few days ago during a two-hour layover.
KLM Crown Lounge Entrance
The lounge is located next to Gate D8 in the international terminal. All terminals are accessible via a post-security monorail.
KLM operates just one outbound flight from Houston: a mid-afternoon 747-400 to Amsterdam. So the lounge is probably not particularly crowded with KLM's own passengers - I'd guess that most of its guests are Priority Pass holders. When I visited around 11:30am, I was one of four passengers in the lounge.
There's plenty of seating with a relatively open floorplan:
In the middle of the lounge, there is an island with food and drinks and a dining area.
The food wasn't very extensive, but (1) it's still better than a U.S. domestic-carrier lounge, and (2) there weren't that many mouths to feed. The lunch service featured a cold pasta salad, small sandwiches, fruit, crudités, and corn chowder (mislabeled as lobster bisque).
Bottom line: the lounge is perfectly serviceable but unremarkable. It doesn't have any unique character and the food isn't exciting or particularly appetizing. But it's a fine place to grab a sandwich and a soda and do a bit of work while you wait for your connecting flight.