Why are the PP models a pain to paint?
Aside from the poses meaning they have to be cast as multipart figures that don't go together very well and need a fair bit of putty to hide the joins, they have a habit of being cluttered with oversized weapons and kit that really gets in the way and which I find quite annoying.
For example, the guy in the blue-ish armour is loaded down with a sword, bolo/chain thing, a bow and quiver and what appear to be two spellbooks crammed into the pockets of his overcoat. I'm sure there's a reason for it in game terms, but from an aesthetic point of view it looks like the sculptor was playing Equipment Buckaroo and tried to pile as much on as he could before the spring sprung.
Contrast that with the Red Box figures, who also have a lot of equipment. But in this case it looks like it belongs and doesn't get in the way of the figure's posing.
To be fair, the PP figs are well sculpted, they are just a bit overblown for my taste.