Just finished the last episode for the second time, final thoughts:

• Dale/Richard never identified himself as Richard 
• Piage/Laura seemed to identify a connection with the name Sarah, even the way she says the name
• Laura clearly responded to what sounded like Sarah's calling for her at the end
• Cooper's ability to determine Laura worked at Judy's dinner without meeting her is beyond reason
• Copper seems to be seeking something unseen out on the street in Twin Peaks
• The lights and flash at the end suggests something outside of reality is going on

I think this last point is my main hang up with the idea that the final 30 minutes are the true reality.  In fact it suggests to me Richard is not the real Dale.  This along with Laura's response to hearing someone yelling her name.

Posted by: Joshua Moulinie

I think Coop's changing attitude is just a sign that his constant battle with these forces is slowly breaking his spirit.
While he is still good, and will not quit trying to save Laura and the world, the chirpy talkative Coop has been worn out by his constant defeats at the hands of evil.
I viewed it as a 'right, time to get serious, no more fucking about.'

I've been thinking the same thing about Cooper on rewatch today. He seems less like "a different person" and more like a changed one (in a more normal way that people changed during or after life-changing events). The guy in fact should be catatonic from all the stress. That he isn't is due to his training. He seems to be in some kind of hyperfocus as we see in the Judy's Diner scene. 

Also, I'll just put it out there--the sex scene with Diane seems less "dark" to me than it did on first watch. It seems very adult. It's not romantic in any way, and that is what threw me off (also Lynch deliberately creates a dark mood with the ambient sound behind the song). The sadness of Diane seemed more like an explosion of emotion pent up (she also senses a big change coming and perhaps their separation) and Cooper seemed more like he was trying to remember her face--he never took his eyes off it. I'm starting to think this is an effort to introduce adult sexuality between middle-aged people who know each other (with a foreshadowing of separation) into the candyland of American TV, and it looks weird because we either get it dressed up as true romance or served up as rape.

You are just begging for abuse, aren't ya?  😉

Posted by: numt3

Or is it possible that what we are seeing is the evolution of Cooper INTO Mr C?

Not sure how this works in terms of doppelgangers, but could Mr C in episodes 1-17 be the future Cooper, returning to Twin Peaks to complete his mission?

We still aren't entirely sure what he was after......

I had that feeling too.  Not sure whether that is actually happening or if we are just supposed to be recognizing traits of Mr. C in Richard/Cooper.  Certainly makes the sex scene with Diane all the more disturbing.