I had no problem with his fight with Finn. As you said, he besmirched him. I would have had no problem with Rey using the Force to hurt Ren enough to allow her to escape. The problem is she absolutely
smashed him. Even allowing for the extent of his injuries, this means I struggle to see him as a credible Big Bad. Yes, he was wounded. Yes, he still needs to complete his training under Snoke. But the next time he and Rey throw hands, she will be much more skilled and powerful in the Force, having gone through Jedi Camp under Luke himself.
That's one reason I hope they go the cyborg route, making him physically stronger, while Snoke finishes his Dark Side training.
I want to see Rey get her ass handed to her in the rematch by Kylo 2.0, thus setting up a deciding fight in the third movie. Ridley is a fine actress. But at this point, Rey is too overpowered to build a convincing sense of threat.
Oh, and for the love of the Force - no more fucking Death Stars! It's the Star Wars equivalent of invading Russia in the winter. It never works.