It's a fairly straightforward cake to make, but I did find it to be quite time consuming, and very messy when it came to applying the oreo crumbs to the side of the cake. I was worried that the biscuit crumbs would go stale overnight (I made the cake on Friday and it was eaten at a party on Saturday) but there were no complaints.
The cake itself was four layers of 8" square chocolate cake with chocolate buttercream inbetween. You need to apply the oreos while the buttercream is still soft so don't put it in the fridge to firm up or the crumbs won't stick. I used three sleeves of oreos with the cream scrapped off for the crumbs. The top was buttercream dyed green. Definitely watch the youtube tutorial and it was very, very helpful.