Some spoilers in this post so look away if you haven't seen the movie
What I mean by "lost credibility" is that before the mask came off, he was the Most intimidating villain of the series for me. Might have been smaller than Darth Vader in stature but
1. The mask looked sick
2. His voice in the mask (at least in the german Version) was deep
3. It was acted out very well, the whole posture of the actor and the way he loses it after getting bad news makes him a really convincing villain, then he takes off the mask and just becomes kinda soft.. this is also not aided by the fact he loses a battle against Rey who hasn't even received Basic Training while he has been trained by the Most powerful sith lord of his era.
blasphemy!
most intimidating? no way. Vader was more intimidating. But I think the most intimidating to date is Maul. They really let an awesome character slip. Maul is the Khal Drogo of a galaxy far far away and Khal Drogo is the Darth Maul of Westeros.
Ren's mask was ok, but it was too dirt bike helmety for me. His light saber was cool but the hand/cross guard had no purpose. it was just there to look cool, which it was.
voice was good, demeanor was good. But when he lost his temper i felt it made him look emotionally weak. when someone failed Vader he rape choked them with the force, not throw furniture around and slash up his office.
i agree with krich though, he nailed his first scene. that was a badass entry scene, set up a great tone with his character and that's why people are disappointed that it fizzled out toward the end
