I remember really enjoying The Return but everything else being pretty "meh."
I remember really enjoying "The Ashes of Eden", both the hardcover and the comic adaptation.
"The Return" is a pretty gripping page turner, but the returned Kirk is not really the Kirk we knew, and the ending made me angry. However, the Kirk we meet in "Avenger" has become SuperKirk, the being who one day will give Worf a run for his credits.
The "Mirror Universe" trilogy isn't too bad, and it starts out really well. But Shatner seemingly has a change of heart about using one particular guest character, who kinda vanishes from the action in the middle of a book.
The best thing about the "Totality" trilogy, set in the 24th century, are the 23rd century flashbacks. Maybe he shoulda just concentrated on 5YM stories after the MU, instead of trying to cultivate a new Kirkling for the Next Generation?