When we were in Colchester we spent almost a full day in the Castle Museum. We had visited the castle grounds on the previous evening and were keen to explore the museum when it was open the following morning.
The displays in the museum were excellent and I specifically liked the fact that serious trouble had been taken to ensure that the exhibits catered for children.
The quality of the exhibits was outstanding and many of the pieces would rival those in the British Museum in London.
Unfortunately if you want to visit the museum today it is not possible as the museum is closed until Spring 2014. Exhibits are being redeveloped and the fabric of the building repaired. You will need to delay your visit until it reopens.
Gippsland Granny 
Looks like it’d be worth waiting for though!