I am an architect, solo traveller and went here for three hours - this is far too little time! Look at it as a huge park with hills, water, open green spaces, woods and lake view. Amidst this scenery they assembled a great collection of buildings from the Meiji period when Japan opened to western culture, so you see Japanese architecture with new elements and buildings by western architects for Japanese places (Frank lloyd Wright's lobby of the Imperial Hotel in Tokyo!!!). The buildings are NOT cardboard, they were just relocated, so all of them are fully visible interior and exterior and are furnished and decorated in the style of their time. You can touch mostly everthing, sit down on the furniture etc. The buildings also are very nicely set and have the space they need, some are located on hills, some have plazas etc. There are administrative buildings, residential, functional, industrious ones, bridges, two churches etc. Some buildings have frequent and free guided tours by exceptionally well-english speaking guides who really know their building. All of the buildings have displays with floor drawings, facts and a good English text, even if you don't know any Japanese, you'll be fine. Inside some buildings there are additonal exhibitions, too. All throughout the 'park' there are cafes and restaurants nicely integrated - go have a coffee in the Imperial hotel lobby! The entrance fee of 1400 for an adult is more than ok for all of this. There are green playing fields and frequent rest areas, too, so it is great place to take kids. Bring a picknick, food might be a bit pricier (haven't checked myself).
You can get here by bus from Inuyama and also from Nagoya directly.
If I had time, I would certainly go again! Right now!