It was a great episode! I don't know if it was good enough as a season opener, but definetely good enough as individual episode.
The whole story, and the way we saw it, was original and good enough to make a great episode. The whole "Open Door" thing, the dinamic of the episode, the scenes and the story itself were amazing. The story has a very "quick" theme. First searching Paige, then trying to save her, then trying to "exorcist" her! It has no boring scenes were they are sit there and doing nothing! Anyway, It would have been great see them with more about Prue, we only see the Phoebe's bad sad scene. I hate so much this scene, despite the fact that I didn't like the acting, I didn't like the dialogue: It was like "I don't miss Prue, I am only scared because I am gonna die"
The whole effects and story in this episode was so damn great! Love the scene when Piper goes downstairs trough the mark of stairs and then with no cuts she goes down rolling :D It was one of the best stunts scenes in the whole story of Charmed! Love it! We see the Source by the first time! And we see the schoking power thingy and the make you fly too! So why he didn't use it in the Charmed and Dangerous episode??? I think that some episodes like this one make the whole Dangerous and Charmed (I wrote it badly!) looks like a "stupid" finale for the Source.
The stunt work was not the only great thing in this episode. I loved the spell think about see what is under the face! You know what I mean... To end, the off-screen camera was awesome! I really loved the scene when Paige throws a lamp to the sister, and a lot of scenes were filmed this way! :D And we see a great photography in this episode, usually the photography is normal, here we can see it clearly, specially in the attic scene! And, I have never say that, cause usually is not a big big thing... but I loved the costume work! Piper looked amazing and so did Phoebe! So I think that the episode is very enjoyable and with tons of action so... 9 one! It is not a 10 because some things were kinda forced, like saving cole with the whole "I am half-whitelighter" thing, and the ending, Prue's dead and Phebe says "We can be sad the rest of ours lifes!!!" For God's sakes no one would never say that! I really loved when we saw that the mother is the one that hits the son! Great