The structure is solid and really easy to put together AND take apart. My kitten LOVES the top bit and will play forever and ever running up and down.  
Now the material isn't great. The top pearch has fabric sides, not floppy, but bendy sides. I don't have a problem with this but it might get destroyed very fast. MY BIGGEST COMPLAINT is the hide, it was the hardest to put together and does not have hard sides, just fabric.
Overall my cats love it and that's all that matters, but longevity might be its downfall.