Not sure whether "over the top" was meant as a complaint; I visited last summer, and thought the (obviously expensive) displays were pretty effective. The main grounds of the museum (the "tourist operation") also now has a bunch of interesting working replica gear, including a Bombe and some of its less publicized support equipment.
The computing museum is also interesting; BTW, in addition to the Colossus rebuild, they're also constructing a working EDSAC replica (using metallic delay lines instead of mercury tanks for memory, but otherwise as exact as possible), and have a bunch of other interesting old machines in the collection. For visit planning, though, it's open fewer days than the Trust-managed property.
I know this is possibly the saddest thing anyone has ever said, but the computing museum is one of my favourite places on earth.
It's a joyful place with so much old technology yet a refreshingly hands on attitude. I don't think there was a single exhibit that wasn't interactive by one method or another - which really matters when you're talking about technology that is largely at an age where kids are too young to have grown up with so it gives them a chance to play with the predecessors to their much loved consumer hardware - and it gives us adults a chance to do more than just reminisce about the fun days experimenting with emerging technologies.
I'd highly recommend that museum on it's own merit; let alone spending the day exploring the site and Bletchly Park as well.
On the subject of early technology I highly recommend 'The Centre for Computing History' in Cambridge. They have a good collection and a lovely atmosphere.
They're currently located in an industrial estate in Cambridge, I'm sure if/when they move they will get much more attention.
Mercury delay lines are literally tanks of liquid, which are prone to leaks, sometimes without warning. Dangerous anywhere, particularly ill-suited to a museum kids may visit.
As to architectural properties, the main thing that they want out of them is that they delay signals by the same number of microseconds; arranging that is not a problem.
The computing museum is also interesting; BTW, in addition to the Colossus rebuild, they're also constructing a working EDSAC replica (using metallic delay lines instead of mercury tanks for memory, but otherwise as exact as possible), and have a bunch of other interesting old machines in the collection. For visit planning, though, it's open fewer days than the Trust-managed property.