Our cats (one is very small, one is very large) were quite happy to get this after we had to throw out their old one when we moved. They kept trying to play on it as we built it. It is a bit shaky if you have a cat on the top portion and another on the bottom and we’re trying to find cinderblocks or something else to weigh it down once and for all (we’ve tried books and things, while that works when the small cat is on the top, the big cat still manages to shake it now and then and we worry). 
The little cave is surprisingly spacious (big cat likes that part best) and the tallest platform is perfect for cats who like to perch. The small cat figured out the IQ box quickly and is no longer interested, but our big cat is still working on it.