We have 6 cats- 5 two-year olds and a 13 year old. They do love the cat tree and play with it everyday. It always seemed top-heavy though and rather shaky; I was worried that eventually it would topple over and either hurt one of our girls or break beyond repair. 

We went to the hardware store and purchased two thin 6 foot boards and some scrap carpet, covered the boards and attached them from the top little house to the base on the back. It stabilized it a lot and now it's a lot more sturdy. 

We also removed half of each ladder, using them as supports for even more stability, as they were covering most of the tops of the little houses where our girls wanted to nap. One of our 6 likes the little baskets, the rest are too wary of climbing into them. 

All in all though, they enjoy it and for the price- it's a good tree. Be prepared to maybe add a few things here and there though to make it safe for your cats if they are hyper like ours.