My cats love this cat tree.  I've recently read that vertical structure is good for cats -particularly, multi-cat households.  This baby does the trick.  I can tell that navigating the platforms, etc. -and, yes, the vertical structure, has introduced a "new dimension" to our cats' lives.  Irritability seems to have been reduced and hierarchical issues seem to be getting resolved by vertical positioning. 

And it's made of plywood -not pressed particle board.