They have improved, but they've also gone through different kinds of knee joints. Some are great, others like the ratchet and rubber knees are awful. I wish I knew which figure had what kind of knees as I'd be buying up the loose bodie en-mass until Sideshow settles on one good design
Probably the biggest critigue overall on the the Prometheus is the forearms are a bit too short and the gap at back of the thighs below the butt is unsightly and not good for tight fitting clothes. Having said that I've used them quite a few time to upgrade older Sideshow figures and have been happy with them.