As a visitor from the USA, I found the IWM collection to be quite different than what I expected, based on my visits to American museums covering the same period/topic. Unlike the US museums I have visited which have large collections of tanks, aircraft, weapons, etc., the IWM featured select exhibits of artifacts with descriptions unique to the history of the items on display. It would have appealed to my interest in WW2 history to see, for example, a life size example of the "tunnel rats" of Tobruk with a description of their contribution to the campaign in North Africa. But, that's just me. On the whole, give yourself 2-3 hours to visit and study the unique collection and read the stories behind the exhibits.