Even if you never make it into the museum exhibits, the architecture and gardens alone are worth a visit. It is all incredibly well thought out and has a very calming effect.
There is also a ton of beautiful and thought provoking artwork there. I jotted down a few artists/pieces that really struck me for different reasons-
Thomas Rowlandson had an ink and watercolor work exhibited (it was different than the one above, but same style). I'm always a fan of caricature and it is intriguing to see such comedic work going on in the 1700's. -Beware if you look this guy up, though, as some of his work is verging on pornographic.
This piece, Portrait of Jeanne Kefer, by Fernand Khnopff is just brilliant. The pale, cool pallet contrasting with her warm figure and the space emphasizing how small she is is just perfect.
Baronne de Domecy by Odilon Redon is such a unique portrait. The sitter is rendered in a realistic manner and in very bland tones while the background is free and verging on abstract. I think this work struck a chord with me because I have been struggling to push beyond following photographic reference to the detail and, instead, creating a piece that is overall visually harmonious.
I think this Redon quote (found on Wikipedia) is interesting -"I have often, as an exercise and as a sustenance, painted before an object down to the smallest accidents of its visual appearance; but the day left me sad and with an unsatiated thirst. The next day I let the other source run, that of imagination, through the recollection of the forms and I was then reassured and appeased."
Hope this post isn't boring; I know it is a bit more wordy than usual!