Despite the reviews that suggested that Mini-Europe was primarily for kids, my wife and I thoroughly enjoyed it. Perhaps we're just kids at heart! The attraction is located in the Brupark, the same park as the Atomium and a water park. It is easy to get to if you take the subway or trams to the Heizel stop.
Mini-Europe is a collection of models of the most famous sights throughout the various countries in the European Union. Everything, with a couple of exceptions, is built to 1/25th scale, so you can see how they compare to each other in terms of size. The detail is incredible, and the movements and other additions are a nice touch. The models are aligned with their counterparts in their respective countries, i.e. all of the sights in the UK are right near each other. At the entrance to each country, you can push a button and hear the national anthem. At other areas, you can push a button to make Mt. Vesuvius erupt or other little animations happen.
At the entrance, they give you a small booklet which gives data about each of the countries. The booklet also explains the significance of each of the models and in some cases, how long it took to make them. The booklet is more or less laid out in the same order as the exhibits, so it is pretty easy to follow along and read as you go. At the end of the tour along the park, there is an exhibit where you can play video and trivia games to learn more about the EU. As something that is a still evolving process, it was very interesting to learn about the goals and processes involved in creating a unified Europe.
The price for admission into the park in combination with the Atomium was 15.50 euro per person. The Atomium wasn't that impressive, but Mini-Europe was definitely worth it. Whether you have children or not, you should definitely go and check it out. In addition, there are a number of good restaurants in the Brupark that are pretty cheap compared to downtown Brussels. Check out the entry on the Happy Corner for a recommendation of a good restaurant.