Ive done alot of Models in my time, and the hardest things i have ever done were from Forgeworld for Warhammer 40k.
Ignore the fact that it looks easy, and looks like mostly big pieces, (there are some really tricky bits too)
This stuff is so fucking hard to put together.
For some reason, there are always warped parts and loads of parts that over fit, sometimes (ive never ecountered this but friends have) bitz that don't meet, to you have to go all plasticard + green stuff johnny commando with the kits.
Often takes hours of filing stuff down to match up properly, submerging parts in hot (but not too hot) water, and bending and warping the components back into their actual position, and hours and fucking hours and hours and hours and more hours of filing shit to meet up.
You finally have something that looks fucking awesome and is actually somehow worth it!!