I was just at the Imperial War Museum in London back in May...to me, it left much to be desired. Overall, most of the exhibits were underwhelming.
Ironically, on the first floor of the IWM is a utterly smashed up car from Iraq that was shattered in a car bombing (VBIED), which killed about 80 people —now that was the one exhibit that really did show what real terrorists are all about.
They have a wonderful WWI section in which you walk through the trenches. And their Holocaust section was upsetting. I plan to return to it next year as I’m planning a two week visit to England.