I had an NPC Penumbral Lord. Admittedly he wasn't evil or good, (TN) but he was in contest with a local lord (in actuality a powerful lich). I didn't get to use him in combat, but these are my impressions of Penumbral Lord:
1: I think the spell progression is a little off. I'd perfer something like Mirror Master. That way you still get a lot UMPH when you cast spells.
2. It could use a few more powers. I had a revised version of Penumbral Lord (I lost it though) that allowed him to open small gateways into the Plane of Shadow and summon shadows. Plus he could also turn into a shadow creature as well. These were obviously high level powers (8th and 10th respectively)
3. Overall, Penumbral Lord is a great little Pr-class but not as powerful as some others. Course shadow magic isn't supposed to be like tossing fireballs at will, but still, I think a revision wouldn't hurt to help give a Penumbral Lord more power. Course I'd add more requirements but nothing major.