It really needs some polishing, but I am using a handcrafted UserScript [1] that lets me navigate comments with the keyboard (j/k as well as p/g/J/K), fold/unfold (m) and vote (a/z). Also some styling to ease reading (larger font, indentation marker). However, the "reply" (r) feature is not complete (i.e. broken), "last" (G) shortcut fails for some reason and flagged comments break the navigation.
If you look in the relevant folder, you may notice it was initially designed for Word Press (WP.user.js), more precisely SlateStarCodex, and seems to work for most such blogs. SSC.user.js is just meant to improve the styling of SlateStarCodex.