I believe, that "The Return", would've been, and could've been, an excellent movie. Certainly TNG's second best, if handled properly. And a better send-out to Kirk than that atrocity that generated the novel in the first place.
However, despite loving the novel, I'm not blind to its flaws. While not as Kirk-centric as "Avenger" or "Preserver" later were, it still has problem that hurt its structure. So here's the changes I'd offer:
0) Using that opening from Trek III, start with Picard finding Kirk's body and then going all the way through to where the camera pans up after seeing Kirk's grave. We hear Shatner do the opening as it is for TNG. Then we hear the main theme from Trek III, as we all of Veridian III. A time lapse as the day turns to night and ending with the camera paning back down to Kirk's grave. Spock standing over it, just like in the book. We see Riker and the Away Team from the Farragut (sp) beam down. The camera closes up to Riker as he looks at Spock. Then we see his point of view. As it closes up, we hear the end of the opening theme. Which matches up in Trek III as when Kirk is standing in the turbolift after leaving the bridge.
1) No Worf. Maybe one scene where Borg-Kirk wants to ask him questions, but such scene won't be like in the novel: Worf is off to deliver Alexander to the Rozehnkos, on a space station (not DS9) following the Enterprise's fall, just before he's off for that monastery he mentioned he were in "The Way of the Warror". Worf feels Kirk coming, and they fight. Unlike the novel, Kirk loses to Worf, and Worf never learns he kicked Kirk's butt, as he's transported back from Salatrel (the novel's main villain). After that, we don't see Worf again.
2) Geordi has no visor in this story. As a result of the Ent-D incident, he decides to have his eyes be as they will be, retroactively speaking, in "First Contact. Have his and Data's expedition on Trilex be Geordi's first demonstration on those "new" eyes of his.
3) Insert a Picard-Crusher scene when they're travelling on the Borg cube in transwarp speed, with Picard explaining his feelings over the loss of Ent-D, the 8 years above it, and his own state of loss for his brother and nephew. A meaty scene for Picard, in general.
4) Flesh out Data a bit. Have him experience an emotional breakdown while on DS9, as he accesses his memories of the previous 10 years, and refers to Lal and Lore and all those events that, with the emotion chip in place, have gotten to hurt him. I essentially propose for Ronald D. Moore's original idea to be used here. It'd be a great scene, provided its not played for laughs, of course.
5) Have one definite Big Three scene, after Spock-Kirk-Picard have had the mind melded. Have Spock and Bones discuss how it was for these 80 years he was away. How they coped with his loss, and how Spock always maintained he never died. Have Kirk aknowledge his mistakes and falls, and his sense of guilt over what he did when in Borg mode.
6) Expand a little on that scene with Picard-Kirk, where they talk about their ships. Have mentions to Kirk's son, David, and his brother, George Samuel, in relation to Picard's loss of Robert and Renie.
7) Absolutely keep the V'Ger-Borg connection.
8) Instead of Kirk's maneuver saving the day, have Picard do the "Picard maneuver", slightly altered though, thus giving him a good part.
9) Of course, have a Sovereign class starship assigned for the Borg homeworld mission ahead - strongly implying that this will end up being the next Enterprise.
10) The transwarp drives on the new ship, because of the incompatible technology, will only serve to bring the Enterprise crew to the Borg Homeworld, and back to Federation - thus explaining that, Federation didn't have a chance of replicating this kind of technology.
11) Once the Borg homeworld is destroyed, have a brief silence over the sacrifice of Kirk, then have a Picard-Riker scene, where we see Picard finally coming to terms with his family's deaths, and tying up those loose ends from GEN (which GEN obviously didn't).
12) Afterwards, have Data assigned to escort Ambassador Spock back to Romulus, and then, have Riker tell Picard that Spock's not convinced that Kirk's dead. When Picard says "There are always, possibilities", the camera pans to space. Then, we hear the "Space, the final frontier" speech, done similarly as in the TNG one, this time by Patrick Stewart. As he says "To boldly go where no one has gone before", the Sovereign-class starship goes to warp, and credits.
Overally, "Star Trek: The Return" would have been an excellent movie. Of course, it would've been cool to adapt all of Shatner's Trek novels, but the absences of Dr McCoy and Scotty would really be felt. It would serve as a great bridge movie, solidifying the necessity of the desperate time-travel scheme hatched by the Borg in "First Contact" - and giving "The Motion Picture" an anchor to the other films that even the Director's Edition seems to lack, thus making the movies as a whole, a series of their own, instead of the one-off adventures they have ended up being after VI.
