The museum is well-done and some of the artwork is...

The museum is well-done and some of the artwork is fantastic. For example, seek out the portrait of William Shakespeare which is the oldest portrait in the museum's collection. This museum has many, many (and even more many) portraits.

The museum is delightfully free of charge.

I'm rating it just four stars because they constantly advertise for tourists to come to the National Portrait Gallery, to see portraits of everyone they know. The cold cruel fact is that most foreign tourists will have no earthly idea who most of the portraits are. If you're from the U.K. or a student of their history, you'll know many (but still not even most) of the people depicted. This paragraph comments only on the fact that the advertisements show a few well-known people and promise even more, when in actual fact you are likely to know ONLY the people whose portraits are in the advertisements.

Definitely go to the National Gallery just around the corner. If you've seen most of the National Gallery and you find yourself saying "I wish I could look at more paintings", then you'll want to go to the National Portrait Gallery also.