This museum was relatively cheap and therefore worth going if you have a few hours to kill ($10HKD each). However, please do not expect very much from this. There is a lack of maintenance in the overall of the museum. A night of things were broken and a number of updates were not updated (eg. Pluto). It also lacked the "punch" needed to attract children (and adults for that matter) and the staff were generally disinterested in helping you. Access to the Space Museum is also not easy in the sense that you have to detour a fair amount to cross to find a path leading to the Space Museum if you happened to be coming from Tsim Sha Tsui/Jordan side.
ON the positive side, it is a fairly cheap attraction. So if you do not have anything to do and you are bored with shopping, this might be an option.