I think the dreamlike vibe was meant to illustrate how surreal it was from Rick's pov like you say. Their deaths weren't really emotional for me, but Rick's face as Jessie goes down got me. It looked like he was lost..like left the building lost...for a minute, just an expression of utter defeat and helplessness.
Then I was like, Jessie's dead..yay!

 

I wasn't a great fan of Jessie either, but for Rick, she probably was some second chance for a normal life and seeing her go down, destroyed all of that.

 

I thought that the flashbacks were more showing us that it wasn't Jessie's death per se that was crushing Rick. I mean, Rick has lost people before. But it was what she represented. The flashbacks to me had more feeling of "home" and "normal family" to them. When she went down, he lost alot more than a partner.