Well, let me start by saying that I personally don't see the full attraction of the Moshi Monsters and Moshlings - but, my 6 year old son and all of his friends love them (and there are much worse things they could be into, so I'm happy to encourage it!). Having collected the little figures for a while, my son has about 25 to play with, and he plays with them for hours and hours. I was dubious about how much more play he could get out of this product, but he agreed to have it instead of pocket money for 5 wks, so I ordered it.
I was pleasantly surprised by the quality of the treehouse, it's sturdy and the parts you have to clip together do so really well and securely.The favourite part for my son is the little basket 'lift', but I have to say, the noise of that gets a bit grating after a while! He hasn't stopped playing with it since he got it. I've heard him making up stories about the moshlings visiting each other, and am really impressed by the way it has enhanced his play with the figures.
It's quite expensive for what it is (I would have liked there to have been a couple more figures with it, perhaps?), but it's not to big and bulky, and so far, it's been a really big hit with my little boy. He even wants to take it on holiday with us next week!!