My son just received this toy for his birthday. Up to recently, he has not been much of a builder or that into models. This has suddenly changed. (I should have known something was up when he kept wanting to play the game "Mousetrap" over and over...). He's kind of a late bloomer in many areas. But when he takes off with something, it's kind of fast.
Anyway, at age 10, he's able to put this together on his own. He did so without any assistance and was quite pleased with his accomplishment. The fact that it's motorized is wonderful. My son has also put other action figures (not K'NEX or Lego) into the ferris wheel seats. Amazingly, it still balances well and continues to turn, without dropping any of his small figures. I was surprised when other reviewers talked about there being no extra parts. He had several left over. (But I must admit in the few things my son has put together, he always seems to have several parts left over. It doesn't seem to affect how anything looks or works. At least so far... :)
This is our first K'NEX toy, and we'll be getting more. I think the K'NEX Box (or whatever it's called) where you can build multiple things looks good. My son typically has trouble focusing on any kind of work for more than a few minutes, and has an even harder time starting things (homework, chores, etc.). Although this requires lots of persistence and problem solving, it's not work to him. I like that he's able maintain his focus for so long. This is an unusual and welcome development.
For those with younger kids who found this too challenging, put it away for awhile. Take it out in a year or so, and begin work on it yourself. Your kid may come around and want to help with it. I know for working parents this is asking a lot. (After all, I got lucky when my son received this at an age when he could do it on his own. No way he could have done this at age 7 or even 8). But your kid will love tackling something with you.