Yes, the new one looks nice and clean. I think a bit of padding really helps to make it look modern. (yeah, I know this will ruffle some feathers because some people apparently prefer 0px padding on everything)
One thing that always irked me a bit about the old "comment reply" window is that it has a fixed division of the comment you're replying to, and your own reply. Maybe a toggle would be nice? (and it would also be nice if that top window would also show the text from self-posts when I'm writing a top-level comment; that way we would be able to copy/quote from the selftext. IIRC on reddit it only worked when I was replying to a comment)
Thanks for your work! Using Sync here feels like coming home.