Perhaps because the Guggenheim started off as a means of displaying and sharing a private collection, the works you can see there are a bit different from the norm. Like the Museum of Modern Art, the focus is on art from the the 20th century on. But I felt like the Guggenheim had a lot of work from famous artists done before they were famous. Or rather, work from before they solidified the style for which they became famous.
There was a Picasso from before he fully developed his Cubist approach...
...a trio of Seurat paintings from before he'd narrowed his pointillist focus (and enlarged his canvas) to the degree he'd be known for...
...and other historic pieces, not "historic" themselves in the conventional sense, but in showing the history behind the history we know.
That said, the Guggenheim also displayed work from artists in their prime, including a whole area devoted to Kandinsky:
It also had a lot of very current art, which I generally found more intriguing that the contemporary stuff we'd seen at MoMA. There was a massive diorama that looked like a circuit board from afar, but was actually revealed to be an enormous ant farm up close.
Then there was the cheekiest piece in the museum, with an even cheekier name: "America." It was, quite literally, a gold-plated toilet:
Installed in a unisex bathroom of the fifth floor of the museum, this was a functioning toilet that you were allowed to use (or just go in and gawk at, if you were feeling pee-shy).
Despite having spent several hours at MoMA, I was happy to have gone to the Guggenheim too. Both were subtly different and interesting experiences.