Museumplein is actually an open area between the biggest museums in Amsterdam - Rijksmuseum, Van Gogh Museum & Stedelijk Museum. It has beautiful surroundings with fountains & sculptures and the famous Iamsterdam sign(similar to the one at the airport, but more fun here).
But to get a decent photo with the Iamsterdam sign, you need to visit it early as it becomes busy & people are all over it to get pics with no regards to others.
Nevertheless its a beautiful area with good mix of locals & tourists and must be included during the first visit to amsterdam. The place is also near to vondelpark, leidseplein and the canal cruise, so can be included in the day's itinerary.