Eric, I have Wave I (I still need Wave II though).
They're more close to a Gundam, in that they build a super articulated figure, and they're fragile like a Gundam is. They are cool though and 4" scale... Very great detailed sculpts, ok for accessories (well, the Preds were anyway, and the humans look good).
-2 ball/socket shoulders
-2 ball/socket elbows
-2 ball/socket wrists
-2 ball/socket hips
-2 ball/socket knees
-2 ball/socket ankles
-1 ball/socket torso
-1 ball/socket neck
Every joint's held together via an hourglass pin... They are prone to falling apart when posing them but nothing too major. They hold poses and stuff pretty well.
Sculpts are unmatched by anyone, including McFarlane's attempts... They're great. Real skull necklaces on the preds, it's cool.
The humans look BETTER articulated by my eyes, and maybe better constructed. I must have the Marines and Ripley series, plus the "Aliens" aliens look amazing. They got the costume of the alien down right for that film, while the AvP ones are down right for that film... Nice eyes for detail they have instead of just re-issuing S1