Chateau St. Gerlach is the real deal.
This is a first class venue, sure to impress. The rooms are well-appointed, and bags containing soaps, creams, etc (labelled "Monsieur" and "Madame") are a nice touch. The building is historic and there are some quirks -- but these mostly add to the experience. There are safes in the rooms, and a fan (if not air conditioning). It was nice to wake up to the sounds of the cows mooing in the adjacent field.
Staff are extremely attentive and courteous. Everything from the booking experience (including follow up questions by email), to the shuttle from Maastricht to the hotel, dealing with the front desk, being served in the restaurant, etc, was a very pleasant experience.
Be sure to go on a walk or bike ride (if the weather is nice, obviously) around the grounds and surrounding area. The countryside is beautiful and this is one of the few places in the Netherlands that isn't perfectly flat. Even if you just stick to the grounds of the hotel, walk around and enjoy.
The spa/wellness centre is very nice. I quite enjoyed lounging on the sun chairs and going for a steam and sauna. The facilities are not large, but sufficient. The spa treatments that my partner and I ordered were quite average. I have had far better massages elsewhere, and the rooms are separated by curtains only so you can hear other people discussing their experience with their masseurs. If I were to come to this hotel again, I would skip the spa treatments entirely and just enjoy the pool, sauna, and Turkish steam bath, which were very good.
The food is excellent and is what separates this hotel from the pack. Our evening meal at the bistro was wonderful and service was excellent. (My definition of excellent service is basically courteous, timely, and attentive to my needs. I don't want or need a conversation about anything except the meal with my server.) During dinner the General Manager introduced himself and asked about our stay, which was nice. The breakfast buffet was fantastic and tops the other luxury hotels I have stayed in. Everything is very fresh, with a wide variety of items. Small touches separate this breakfast buffet from others: a variety of fresh squeezed juices; fruit salad that is not an afterthought, but that has interesting fruits in it; a very wide selection of bread, cheeses, etc; decent scrambled eggs (so easy to screw up!); and no cheaping out anywhere, every single item was high quality. The food impressed us thoroughly and would be reason enough for us to return to Chateau St Gerlach.
All that said, my detail-oriented self couldn't help but notice: a cobweb on the ceiling of our room, a lack of heating on the bistro patio on a very chilly night (if you know it's going to get cold, have a plan before seating people out there for a 2+ hour dinner!); the occasional interior decoration faux pas (some weird painted border in our bathroom). I didn't even bother checking what the WiFi cost, but I know it wasn't free, and think it is safe to assume (as I have noticed at other luxury hotels) that it was very expensive for no good reason.
These are very small flaws, and all in all, it was a wonderful experience and I would go back anytime. I will be advising my friends to check this place out.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC