Correct me if I'm wrong, but I was under the impression that only Star Trek II: The Wrath Of Khan
was remastered. Also, Paramount only remastered the theatrical version (which even comes to a surprise to Nicholas Meyer on the new audio commentary!) and changed much of the color-timing of that film to a more blueish tint for no particular reason.
The rest of the Blu-Rays have old, heavily DNR'd transfers on them. There are some new bonus features, but many of these are pointless (i.e. the fan round tables and the commentaries by people who didn't work on the films).
The Blu-Rays certainly could be worse, but they're not great.