First off- great model! it really looks like a classic Space Marine. It's really modeled just like them.
You're facing the classic problem of Space Marine Armour. There's no way in hell those guys could even draw their weapons from side holsters with that arm-armour on.
The rear of the Knee joint and the hip shows it really well. How could that guy sit in a chair?
Basicly, unless you want to go into muscle or deal with intersection, you're going to have to tweak the joints to make them useful. You may want to reference Shirow Masamune's work for a good look at the way power armour joints would work.
I should note that this will mean that your Space Marines will look a little unlike the GW versions. Though given how litigious they are, this may be a good thing. But at least you won't have that classic problem where if he shrugs or tries to climb that ladder you see in the background of all those pretty Space Hulk pictures, he won't squeeze his head off like a zit.